Source code for sympy.tensor.tensor

"""
This module defines tensors with abstract index notation.

The abstract index notation has been first formalized by Penrose.

Tensor indices are formal objects, with a tensor type; there is no
notion of index range, it is only possible to assign the dimension,
used to trace the Kronecker delta; the dimension can be a Symbol.

The Einstein summation convention is used.
The covariant indices are indicated with a minus sign in front of the index.

For instance the tensor ``t = p(a)*A(b,c)*q(-c)`` has the index ``c``
contracted.

A tensor expression ``t`` can be called; called with its
indices in sorted order it is equal to itself:
in the above example ``t(a, b) == t``;
one can call ``t`` with different indices; ``t(c, d) == p(c)*A(d,a)*q(-a)``.

The contracted indices are dummy indices, internally they have no name,
the indices being represented by a graph-like structure.

Tensors are put in canonical form using ``canon_bp``, which uses
the Butler-Portugal algorithm for canonicalization using the monoterm
symmetries of the tensors.

If there is a (anti)symmetric metric, the indices can be raised and
lowered when the tensor is put in canonical form.
"""

from __future__ import print_function, division

import functools
from collections import defaultdict
from sympy import Matrix, Rational
from sympy.combinatorics.tensor_can import get_symmetric_group_sgs, \
    bsgs_direct_product, canonicalize, riemann_bsgs
from sympy.core import Basic, sympify, Add, S
from sympy.core.compatibility import string_types
from sympy.core.containers import Tuple
from sympy.core.decorators import deprecated
from sympy.core.symbol import Symbol, symbols
from sympy.core.sympify import CantSympify
from sympy.external import import_module
from sympy.utilities.decorator import doctest_depends_on
from sympy.matrices import eye


class TIDS(CantSympify):
    """
    Tensor internal data structure. This contains internal data structures about
    components of a tensor expression, its free and dummy indices.

    To create a ``TIDS`` object via the standard constructor, the required
    arguments are

    WARNING: this class is meant as an internal representation of tensor data
    structures and should not be directly accessed by end users.

    Parameters
    ==========

    components : ``TensorHead`` objects representing the components of the tensor expression.

    free : Free indices in their internal representation.

    dum : Dummy indices in their internal representation.

    Examples
    ========

    >>> from sympy.tensor.tensor import TensorIndexType, tensor_indices, TIDS, tensorhead
    >>> Lorentz = TensorIndexType('Lorentz', dummy_fmt='L')
    >>> m0, m1, m2, m3 = tensor_indices('m0,m1,m2,m3', Lorentz)
    >>> T = tensorhead('T', [Lorentz]*4, [[1]*4])
    >>> TIDS([T], [(m0, 0, 0), (m3, 3, 0)], [(1, 2, 0, 0)])
    TIDS([T(Lorentz,Lorentz,Lorentz,Lorentz)], [(m0, 0, 0), (m3, 3, 0)], [(1, 2, 0, 0)])

    Notes
    =====

    In short, this has created the components, free and dummy indices for
    the internal representation of a tensor T(m0, m1, -m1, m3).

    Free indices are represented as a list of triplets. The elements of
    each triplet identify a single free index and are

    1. TensorIndex object
    2. position inside the component
    3. component number

    Dummy indices are represented as a list of 4-plets. Each 4-plet stands
    for couple for contracted indices, their original TensorIndex is not
    stored as it is no longer required. The four elements of the 4-plet
    are

    1. position inside the component of the first index.
    2. position inside the component of the second index.
    3. component number of the first index.
    4. component number of the second index.

    """

    def __init__(self, components, free, dum):
        self.components = components
        self.free = free
        self.dum = dum
        self._ext_rank = len(self.free) + 2*len(self.dum)

    def get_components_with_free_indices(self):
        """
        Get a list of components with their associated indices.

        Examples
        ========

        >>> from sympy.tensor.tensor import TensorIndexType, tensor_indices, TIDS, tensorhead
        >>> Lorentz = TensorIndexType('Lorentz', dummy_fmt='L')
        >>> m0, m1, m2, m3 = tensor_indices('m0,m1,m2,m3', Lorentz)
        >>> T = tensorhead('T', [Lorentz]*4, [[1]*4])
        >>> A = tensorhead('A', [Lorentz], [[1]])
        >>> t = TIDS.from_components_and_indices([T], [m0, m1, -m1, m3])
        >>> t.get_components_with_free_indices()
        [(T(Lorentz,Lorentz,Lorentz,Lorentz), [(m0, 0, 0), (m3, 3, 0)])]
        >>> t2 = (A(m0)*A(-m0))._tids
        >>> t2.get_components_with_free_indices()
        [(A(Lorentz), []), (A(Lorentz), [])]
        >>> t3 = (A(m0)*A(-m1)*A(-m0)*A(m1))._tids
        >>> t3.get_components_with_free_indices()
        [(A(Lorentz), []), (A(Lorentz), []), (A(Lorentz), []), (A(Lorentz), [])]
        >>> t4 = (A(m0)*A(m1)*A(-m0))._tids
        >>> t4.get_components_with_free_indices()
        [(A(Lorentz), []), (A(Lorentz), [(m1, 0, 1)]), (A(Lorentz), [])]
        >>> t5 = (A(m0)*A(m1)*A(m2))._tids
        >>> t5.get_components_with_free_indices()
        [(A(Lorentz), [(m0, 0, 0)]), (A(Lorentz), [(m1, 0, 1)]), (A(Lorentz), [(m2, 0, 2)])]
        """
        components = self.components
        ret_comp = []

        free_counter = 0
        if len(self.free) == 0:
            return [(comp, []) for comp in components]

        for i, comp in enumerate(components):
            c_free = []
            while free_counter < len(self.free):
                if not self.free[free_counter][2] == i:
                    break

                c_free.append(self.free[free_counter])
                free_counter += 1

                if free_counter >= len(self.free):
                    break
            ret_comp.append((comp, c_free))

        return ret_comp

    @staticmethod
    def from_components_and_indices(components, indices):
        """
        Create a new ``TIDS`` object from ``components`` and ``indices``

        ``components``  ``TensorHead`` objects representing the components
                        of the tensor expression.

        ``indices``     ``TensorIndex`` objects, the indices. Contractions are
                        detected upon construction.

        Examples
        ========

        >>> from sympy.tensor.tensor import TensorIndexType, tensor_indices, TIDS, tensorhead
        >>> Lorentz = TensorIndexType('Lorentz', dummy_fmt='L')
        >>> m0, m1, m2, m3 = tensor_indices('m0,m1,m2,m3', Lorentz)
        >>> T = tensorhead('T', [Lorentz]*4, [[1]*4])
        >>> TIDS.from_components_and_indices([T], [m0, m1, -m1, m3])
        TIDS([T(Lorentz,Lorentz,Lorentz,Lorentz)], [(m0, 0, 0), (m3, 3, 0)], [(1, 2, 0, 0)])

        In case of many components the same indices have slightly different
        indexes:

        >>> A = tensorhead('A', [Lorentz], [[1]])
        >>> TIDS.from_components_and_indices([A]*4, [m0, m1, -m1, m3])
        TIDS([A(Lorentz), A(Lorentz), A(Lorentz), A(Lorentz)], [(m0, 0, 0), (m3, 0, 3)], [(0, 0, 1, 2)])
        """
        tids = None
        cur_pos = 0
        for i in components:
            tids_sing = TIDS([i], *TIDS.free_dum_from_indices(*indices[cur_pos:cur_pos+i.rank]))
            if tids is None:
                tids = tids_sing
            else:
                tids *= tids_sing
            cur_pos += i.rank

        if tids is None:
            tids = TIDS([], [], [])

        tids.free.sort(key=lambda x: x[0].name)
        tids.dum.sort()

        return tids

    def to_indices(self):
        """
        Get a list of indices, creating new tensor indices to complete dummy indices.
        """
        component_indices = []
        for i in self.components:
            component_indices.append([None]*i.rank)

        for i in self.free:
            component_indices[i[2]][i[1]] = i[0]

        for i, dummy_pos in enumerate(self.dum):
            tensor_index_type = self.components[dummy_pos[2]].args[1].args[0][0]
            dummy_index = TensorIndex('dummy_index_{0}'.format(i), tensor_index_type)
            component_indices[dummy_pos[2]][dummy_pos[0]] = dummy_index
            component_indices[dummy_pos[3]][dummy_pos[1]] = -dummy_index

        indices = []
        for i in component_indices:
            indices.extend(i)

        return indices

    @staticmethod
    def free_dum_from_indices(*indices):
        """
        Convert ``indices`` into ``free``, ``dum`` for single component tensor

        ``free``     list of tuples ``(index, pos, 0)``,
                     where ``pos`` is the position of index in
                     the list of indices formed by the component tensors

        ``dum``      list of tuples ``(pos_contr, pos_cov, 0, 0)``

        Examples
        ========

        >>> from sympy.tensor.tensor import TensorIndexType, tensor_indices, TIDS
        >>> Lorentz = TensorIndexType('Lorentz', dummy_fmt='L')
        >>> m0, m1, m2, m3 = tensor_indices('m0,m1,m2,m3', Lorentz)
        >>> TIDS.free_dum_from_indices(m0, m1, -m1, m3)
        ([(m0, 0, 0), (m3, 3, 0)], [(1, 2, 0, 0)])
        """
        n = len(indices)
        if n == 1:
            return [(indices[0], 0, 0)], []

        # find the positions of the free indices and of the dummy indices
        free = [True]*len(indices)
        index_dict = {}
        dum = []
        for i, index in enumerate(indices):
            name = index._name
            typ = index._tensortype
            contr = index._is_up
            if (name, typ) in index_dict:
                # found a pair of dummy indices
                is_contr, pos = index_dict[(name, typ)]
                # check consistency and update free
                if is_contr:
                    if contr:
                        raise ValueError('two equal contravariant indices in slots %d and %d' %(pos, i))
                    else:
                        free[pos] = False
                        free[i] = False
                else:
                    if contr:
                        free[pos] = False
                        free[i] = False
                    else:
                        raise ValueError('two equal covariant indices in slots %d and %d' %(pos, i))
                if contr:
                    dum.append((i, pos, 0, 0))
                else:
                    dum.append((pos, i, 0, 0))
            else:
                index_dict[(name, typ)] = index._is_up, i

        free = [(index, i, 0) for i, index in enumerate(indices) if free[i]]
        free.sort()
        return free, dum

    @staticmethod
    def mul(f, g):
        """
        The algorithms performing the multiplication of two ``TIDS`` instances.

        In short, it forms a new ``TIDS`` object, joining components and indices,
        checking that abstract indices are compatible, and possibly contracting
        them.

        Examples
        ========

        >>> from sympy.tensor.tensor import TensorIndexType, tensor_indices, TIDS, tensorhead
        >>> Lorentz = TensorIndexType('Lorentz', dummy_fmt='L')
        >>> m0, m1, m2, m3 = tensor_indices('m0,m1,m2,m3', Lorentz)
        >>> T = tensorhead('T', [Lorentz]*4, [[1]*4])
        >>> A = tensorhead('A', [Lorentz], [[1]])
        >>> tids_1 = TIDS.from_components_and_indices([T], [m0, m1, -m1, m3])
        >>> tids_2 = TIDS.from_components_and_indices([A], [m2])
        >>> tids_1 * tids_2
        TIDS([T(Lorentz,Lorentz,Lorentz,Lorentz), A(Lorentz)],\
            [(m0, 0, 0), (m3, 3, 0), (m2, 0, 1)], [(1, 2, 0, 0)])

        In this case no contraction has been performed.

        >>> tids_3 = TIDS.from_components_and_indices([A], [-m3])
        >>> tids_1 * tids_3
        TIDS([T(Lorentz,Lorentz,Lorentz,Lorentz), A(Lorentz)],\
            [(m0, 0, 0)], [(1, 2, 0, 0), (3, 0, 0, 1)])

        Free indices ``m3`` and ``-m3`` are identified as a contracted couple, and are
        therefore transformed into dummy indices.

        A wrong index construction (for example, trying to contract two
        contravariant indices or using indices multiple times) would result in
        an exception:

        >>> tids_4 = TIDS.from_components_and_indices([A], [m3])
        >>> # This raises an exception:
        >>> # tids_1 * tids_4
        """
        index_up = lambda u: u if u.is_up else -u

        # find out which free indices of f and g are contracted
        free_dict1 = dict([(i if i.is_up else -i, (pos, cpos, i)) for i, pos, cpos in f.free])
        free_dict2 = dict([(i if i.is_up else -i, (pos, cpos, i)) for i, pos, cpos in g.free])

        free_names = set(free_dict1.keys()) & set(free_dict2.keys())
        # find the new `free` and `dum`
        nc1 = len(f.components)
        dum2 = [(i1, i2, c1 + nc1, c2 + nc1) for i1, i2, c1, c2 in g.dum]
        free1 = [(ind, i, c) for ind, i, c in f.free if index_up(ind) not in free_names]
        free2 = [(ind, i, c + nc1) for ind, i, c in g.free if index_up(ind) not in free_names]
        free = free1 + free2
        dum = f.dum + dum2
        for name in free_names:
            ipos1, cpos1, ind1 = free_dict1[name]
            ipos2, cpos2, ind2 = free_dict2[name]
            cpos2 += nc1
            if ind1._is_up == ind2._is_up:
                raise ValueError('wrong index construction {0}'.format(ind1))
            if ind1._is_up:
                new_dummy = (ipos1, ipos2, cpos1, cpos2)
            else:
                new_dummy = (ipos2, ipos1, cpos2, cpos1)
            dum.append(new_dummy)
        return (f.components + g.components, free, dum)

    def __mul__(self, other):
        return TIDS(*self.mul(self, other))

    def __str__(self):
        return "TIDS({0}, {1}, {2})".format(self.components, self.free, self.dum)

    def __repr__(self):
        return self.__str__()

    def sorted_components(self):
        """
        Returns a ``TIDS`` with sorted components

        The sorting is done taking into account the commutation group
        of the component tensors.
        """
        from sympy.combinatorics.permutations import _af_invert
        cv = list(zip(self.components, range(len(self.components))))
        sign = 1
        n = len(cv) - 1
        for i in range(n):
            for j in range(n, i, -1):
                c = cv[j-1][0].commutes_with(cv[j][0])
                if c not in [0, 1]:
                    continue
                if (cv[j-1][0]._types, cv[j-1][0]._name) > \
                        (cv[j][0]._types, cv[j][0]._name):
                    cv[j-1], cv[j] = cv[j], cv[j-1]
                    if c:
                        sign = -sign

        # perm_inv[new_pos] = old_pos
        components = [x[0] for x in cv]
        perm_inv = [x[1] for x in cv]
        perm = _af_invert(perm_inv)
        free = [(ind, i, perm[c]) for ind, i, c in self.free]
        free.sort()
        dum = [(i1, i2, perm[c1], perm[c2]) for i1, i2, c1, c2 in self.dum]
        dum.sort(key=lambda x: components[x[2]].index_types[x[0]])

        return TIDS(components, free, dum), sign

    def canon_args(self):
        """
        Returns ``(g, dummies, msym, v)``, the entries of ``canonicalize``

        see ``canonicalize`` in ``tensor_can.py``
        """
        # to be called after sorted_components
        from sympy.combinatorics.permutations import _af_new
#         types = list(set(self._types))
#         types.sort(key = lambda x: x._name)
        n = self._ext_rank
        g = [None]*n + [n, n+1]
        pos = 0
        vpos = []
        components = self.components
        for t in components:
            vpos.append(pos)
            pos += t._rank
        # ordered indices: first the free indices, ordered by types
        # then the dummy indices, ordered by types and contravariant before
        # covariant
        # g[position in tensor] = position in ordered indices
        for i, (indx, ipos, cpos) in enumerate(self.free):
            pos = vpos[cpos] + ipos
            g[pos] = i
        pos = len(self.free)
        j = len(self.free)
        dummies = []
        prev = None
        a = []
        msym = []
        for ipos1, ipos2, cpos1, cpos2 in self.dum:
            pos1 = vpos[cpos1] + ipos1
            pos2 = vpos[cpos2] + ipos2
            g[pos1] = j
            g[pos2] = j + 1
            j += 2
            typ = components[cpos1].index_types[ipos1]
            if typ != prev:
                if a:
                    dummies.append(a)
                a = [pos, pos + 1]
                prev = typ
                msym.append(typ.metric_antisym)
            else:
                a.extend([pos, pos + 1])
            pos += 2
        if a:
            dummies.append(a)
        numtyp = []
        prev = None
        for t in components:
            if t == prev:
                numtyp[-1][1] += 1
            else:
                prev = t
                numtyp.append([prev, 1])
        v = []
        for h, n in numtyp:
            if h._comm == 0 or h._comm == 1:
                comm = h._comm
            else:
                comm = TensorManager.get_comm(h._comm, h._comm)
            v.append((h._symmetry.base, h._symmetry.generators, n, comm))
        return _af_new(g), dummies, msym, v

    def perm2tensor(self, g, canon_bp=False):
        """
        Returns a ``TIDS`` instance corresponding to the permutation ``g``

        ``g``  permutation corresponding to the tensor in the representation
        used in canonicalization

        ``canon_bp``   if True, then ``g`` is the permutation
        corresponding to the canonical form of the tensor
        """
        vpos = []
        components = self.components
        pos = 0
        for t in components:
            vpos.append(pos)
            pos += t._rank
        sorted_free = [x[0] for x in self.free]
        sorted_free.sort()
        nfree = len(sorted_free)
        rank = self._ext_rank
        dum = [[None]*4 for i in range((rank - nfree)//2)]
        free = []
        icomp = -1
        for i in range(rank):
            if i in vpos:
                icomp += vpos.count(i)
                pos0 = i
            ipos = i - pos0
            gi = g[i]
            if gi < nfree:
                ind = sorted_free[gi]
                free.append((ind, ipos, icomp))
            else:
                j = gi - nfree
                idum, cov = divmod(j, 2)
                if cov:
                    dum[idum][1] = ipos
                    dum[idum][3] = icomp
                else:
                    dum[idum][0] = ipos
                    dum[idum][2] = icomp
        dum = [tuple(x) for x in dum]

        return TIDS(components, free, dum)


class VTIDS(TIDS):
    """
    DEPRECATED: DO NOT USE.
    """

    @deprecated(useinstead="TIDS")
    def __init__(self, components, free, dum, data):
        super(VTIDS, self).__init__(components, free, dum)
        self.data = data

    @staticmethod
    @deprecated(useinstead="TIDS")
    def parse_data(data):
        """
        DEPRECATED: DO NOT USE.
        """
        return _TensorDataLazyEvaluator.parse_data(data)

    @deprecated(useinstead="TIDS")
    def correct_signature_from_indices(self, data, indices, free, dum):
        """
        DEPRECATED: DO NOT USE.
        """
        return _TensorDataLazyEvaluator._correct_signature_from_indices(data, indices, free, dum)

    @staticmethod
    @deprecated(useinstead="TIDS")
    def flip_index_by_metric(data, metric, pos):
        """
        DEPRECATED: DO NOT USE.
        """
        return _TensorDataLazyEvaluator._flip_index_by_metric(data, metric, pos)


class _TensorDataLazyEvaluator(CantSympify):
    """
    EXPERIMENTAL: do not rely on this class, it may change without deprecation
    warnings in future versions of SymPy.

    This object contains the logic to associate components data to a tensor
    expression. Components data are set via the ``.data`` property of tensor
    expressions, is stored inside this class as a mapping between the tensor
    expression and the ``ndarray``.

    Computations are executed lazily: whereas the tensor expressions can have
    contractions, tensor products, and additions, components data are not
    computed until they are accessed by reading the ``.data`` property
    associated to the tensor expression.
    """
    _substitutions_dict = dict()
    _substitutions_dict_tensmul = dict()

    def __getitem__(self, key):
        dat = self._get(key)
        if dat is None:
            return None

        numpy = import_module("numpy")
        if not isinstance(dat, numpy.ndarray):
            return dat

        if dat.ndim == 0:
            return dat[()]
        elif dat.ndim == 1 and dat.size == 1:
            return dat[0]
        return dat

    def _get(self, key):
        """
        Retrieve ``data`` associated with ``key``.

        This algorithm looks into ``self._substitutions_dict`` for all
        ``TensorHead`` in the ``TensExpr`` (or just ``TensorHead`` if key is a
        TensorHead instance). It reconstructs the components data that the
        tensor expression should have by performing on components data the
        operations that correspond to the abstract tensor operations applied.

        Metric tensor is handled in a different manner: it is pre-computed in
        ``self._substitutions_dict_tensmul``.
        """
        if key in self._substitutions_dict:
            return self._substitutions_dict[key]

        if isinstance(key, TensorHead):
            return None

        if isinstance(key, TensMul):
            tensmul_list = key.split()
            if len(tensmul_list) == 1 and len(tensmul_list[0].components) == 1:
                # special case to handle metrics. Metric tensors cannot be
                # constructed through contraction by the metric, their
                # components show if they are a matrix or its inverse.
                signature = tuple([i.is_up for i in tensmul_list[0].get_indices()])
                srch = (tensmul_list[0].components[0],) + signature
                if srch in self._substitutions_dict_tensmul:
                    return self._substitutions_dict_tensmul[srch]
            data_list = [self.data_tensmul_from_tensorhead(i, i.components[0]) for i in tensmul_list]
            if all([i is None for i in data_list]):
                return None
            if any([i is None for i in data_list]):
                raise ValueError("Mixing tensors with associated components "\
                                 "data with tensors without components data")
            data_result, tensmul_result = self.data_product_tensors(data_list, tensmul_list)
            return data_result

        if isinstance(key, TensAdd):
            sumvar = S.Zero
            data_list = [i.data for i in key.args]
            if all([i is None for i in data_list]):
                return None
            if any([i is None for i in data_list]):
                raise ValueError("Mixing tensors with associated components "\
                                 "data with tensors without components data")
            for i in data_list:
                sumvar += i
            return sumvar

        return None

    def data_tensorhead_from_tensmul(self, data, tensmul, tensorhead):
        """
        This method is used when assigning components data to a ``TensMul``
        object, it converts components data to a fully contravariant ndarray,
        which is then stored according to the ``TensorHead`` key.
        """
        if data is None:
            return None

        return self._correct_signature_from_indices(
            data,
            tensmul.get_indices(),
            tensmul.free,
            tensmul.dum,
            True)

    def data_tensmul_from_tensorhead(self, tensmul, tensorhead):
        """
        This method corrects the components data to the right signature
        (covariant/contravariant) using the metric associated with each
        ``TensorIndexType``.
        """
        if tensorhead.data is None:
            return None

        return self._correct_signature_from_indices(
            tensorhead.data,
            tensmul.get_indices(),
            tensmul.free,
            tensmul.dum)

    def data_product_tensors(self, data_list, tensmul_list):
        """
        Given a ``data_list``, list of ``ndarray``'s and a ``tensmul_list``,
        list of ``TensMul`` instances, compute the resulting ``ndarray``,
        after tensor products and contractions.
        """
        def data_mul(f, g):
            """
            Multiplies two ``ndarray`` objects, it first calls ``TIDS.mul``,
            then checks which indices have been contracted, and finally
            contraction operation on data, according to the contracted indices.
            """
            data1, tensmul1 = f
            data2, tensmul2 = g
            components, free, dum = TIDS.mul(tensmul1, tensmul2)
            data = _TensorDataLazyEvaluator._contract_ndarray(tensmul1.free, tensmul2.free, data1, data2)
            # TODO: do this more efficiently... maybe by just passing an index list
            # to .data_product_tensor(...)
            return data, TensMul.from_TIDS(S.One, TIDS(components, free, dum))

        return functools.reduce(data_mul, zip(data_list, tensmul_list))

    def _assign_data_to_tensor_expr(self, key, data):
        if isinstance(key, TensAdd):
            raise ValueError('cannot assign data to TensAdd')
        # here it is assumed that `key` is a `TensMul` instance.
        if len(key.components) != 1:
            raise ValueError('cannot assign data to TensMul with multiple components')
        tensorhead = key.components[0]
        newdata = self.data_tensorhead_from_tensmul(data, key, tensorhead)
        return tensorhead, newdata

    def __setitem__(self, key, value):
        """
        Set the components data of a tensor object/expression.

        Components data are transformed to the all-contravariant form and stored
        with the corresponding ``TensorHead`` object. If a ``TensorHead`` object
        cannot be uniquely identified, it will raise an error.
        """
        data = _TensorDataLazyEvaluator.parse_data(value)

        # TensorHead and TensorIndexType can be assigned data directly, while
        # TensMul must first convert data to a fully contravariant form, and
        # assign it to its corresponding TensorHead single component.
        if not isinstance(key, (TensorHead, TensorIndexType)):
            key, data = self._assign_data_to_tensor_expr(key, data)

        if isinstance(key, TensorHead):
            for dim, indextype in zip(data.shape, key.index_types):
                if indextype.data is None:
                    raise ValueError("index type {} has no components data"\
                    " associated (needed to raise/lower index)".format(indextype))
                if indextype.dim is None:
                    continue
                if dim != indextype.dim:
                    raise ValueError("wrong dimension of ndarray")
        self._substitutions_dict[key] = data

    def __delitem__(self, key):
        del self._substitutions_dict[key]

    def __contains__(self, key):
        return key in self._substitutions_dict

    @staticmethod
    def _contract_ndarray(free1, free2, ndarray1, ndarray2):
        numpy = import_module('numpy')

        def ikey(x):
            return x[1:]

        free1 = free1[:]
        free2 = free2[:]
        free1.sort(key=ikey)
        free2.sort(key=ikey)
        self_free = [_[0] for _ in free1]
        axes1 = []
        axes2 = []
        for jpos, jindex in enumerate(free2):
            if -jindex[0] in self_free:
                nidx = self_free.index(-jindex[0])
            else:
                continue
            axes1.append(nidx)
            axes2.append(jpos)

        contracted_ndarray = numpy.tensordot(
            ndarray1,
            ndarray2,
            (axes1, axes2)
        )
        return contracted_ndarray

    @staticmethod
    def add_tensor_mul(prod, f, g):
        def mul_function():
            return _TensorDataLazyEvaluator._contract_ndarray(f.free, g.free, f.data, g.data)

        _TensorDataLazyEvaluator._substitutions_dict[prod] = mul_function()

    @staticmethod
    def add_tensor_add(addition, f, g):
        def add_function():
            return f.data + g.data

        _TensorDataLazyEvaluator._substitutions_dict[addition] = add_function()

    def add_metric_data(self, metric, data):
        """
        Assign data to the ``metric`` tensor. The metric tensor behaves in an
        anomalous way when raising and lowering indices.

        A fully covariant metric is the inverse transpose of the fully
        contravariant metric (it is meant matrix inverse). If the metric is
        symmetric, the transpose is not necessary and mixed
        covariant/contravariant metrics are Kronecker deltas.
        """
        # hard assignment, data should not be added to `TensorHead` for metric:
        # the problem with `TensorHead` is that the metric is anomalous, i.e.
        # raising and lowering the index means considering the metric or its
        # inverse, this is not the case for other tensors.
        self._substitutions_dict_tensmul[metric, True, True] = data
        inverse_transpose = self.inverse_transpose_matrix(data)
        # in symmetric spaces, the traspose is the same as the original matrix,
        # the full covariant metric tensor is the inverse transpose, so this
        # code will be able to handle non-symmetric metrics.
        self._substitutions_dict_tensmul[metric, False, False] = inverse_transpose
        # now mixed cases, these are identical to the unit matrix if the metric
        # is symmetric.
        m = Matrix(data)
        invt = Matrix(inverse_transpose)
        self._substitutions_dict_tensmul[metric, True, False] = m * invt
        self._substitutions_dict_tensmul[metric, False, True] = invt * m

    @staticmethod
    def _flip_index_by_metric(data, metric, pos):
        numpy = import_module('numpy')

        data = numpy.tensordot(
                metric,
                data,
                (1, pos))
        return numpy.rollaxis(data, 0, pos+1)

    @staticmethod
    def inverse_matrix(ndarray):
        m = Matrix(ndarray).inv()
        return _TensorDataLazyEvaluator.parse_data(m)

    @staticmethod
    def inverse_transpose_matrix(ndarray):
        m = Matrix(ndarray).inv().T
        return _TensorDataLazyEvaluator.parse_data(m)

    @staticmethod
    def _correct_signature_from_indices(data, indices, free, dum, inverse=False):
        """
        Utility function to correct the values inside the components data
        ndarray according to whether indices are covariant or contravariant.

        It uses the metric matrix to lower values of covariant indices.
        """
        numpy = import_module('numpy')
        # change the ndarray values according covariantness/contravariantness of the indices
        # use the metric
        for i, indx in enumerate(indices):
            if not indx.is_up and not inverse:
                data = _TensorDataLazyEvaluator._flip_index_by_metric(data, indx._tensortype.data, i)
            elif not indx.is_up and inverse:
                data = _TensorDataLazyEvaluator._flip_index_by_metric(
                    data,
                    _TensorDataLazyEvaluator.inverse_matrix(indx._tensortype.data),
                    i
                )

        if len(dum) > 0:
            ### perform contractions ###
            axes1 = []
            axes2 = []
            for i, indx1 in enumerate(indices):
                try:
                    nd = indices[:i].index(-indx1)
                except ValueError:
                    continue
                axes1.append(nd)
                axes2.append(i)

            for ax1, ax2 in zip(axes1, axes2):
                data = numpy.trace(data, axis1=ax1, axis2=ax2)
        return data

    @staticmethod
    def _sort_data_axes(old, new):
        numpy = import_module('numpy')

        new_data = old.data.copy()

        old_free = [i[0] for i in old.free]
        new_free = [i[0] for i in new.free]

        for i in range(len(new_free)):
            for j in range(i, len(old_free)):
                if old_free[j] == new_free[i]:
                    old_free[i], old_free[j] = old_free[j], old_free[i]
                    new_data = numpy.swapaxes(new_data, i, j)
                    break
        return new_data

    @staticmethod
    def add_rearrange_tensmul_parts(new_tensmul, old_tensmul):
        def sorted_compo():
            return _TensorDataLazyEvaluator._sort_data_axes(old_tensmul, new_tensmul)

        _TensorDataLazyEvaluator._substitutions_dict[new_tensmul] = sorted_compo()

    @staticmethod
    @doctest_depends_on(modules=('numpy',))
    def parse_data(data):
        """
        Transform ``data`` to a numpy ndarray. The parameter ``data`` may
        contain data in various formats, e.g. nested lists, sympy ``Matrix``,
        and so on.

        Examples
        ========

        >>> from sympy.tensor.tensor import _TensorDataLazyEvaluator
        >>> _TensorDataLazyEvaluator.parse_data([1, 3, -6, 12])
        [1 3 -6 12]

        >>> _TensorDataLazyEvaluator.parse_data([[1, 2], [4, 7]])
        [[1 2]
         [4 7]]
        """
        numpy = import_module('numpy')

        if (numpy is not None) and (not isinstance(data, numpy.ndarray)):
            if len(data) == 2 and hasattr(data[0], '__call__'):

                def fromfunction_sympify(*x):
                    return sympify(data[0](*x))

                data = numpy.fromfunction(fromfunction_sympify, data[1])
            else:
                vsympify = numpy.vectorize(sympify)
                data = vsympify(numpy.array(data))
        return data

_tensor_data_substitution_dict = _TensorDataLazyEvaluator()


[docs]class _TensorManager(object): """ Class to manage tensor properties. Notes ===== Tensors belong to tensor commutation groups; each group has a label ``comm``; there are predefined labels: ``0`` tensors commuting with any other tensor ``1`` tensors anticommuting among themselves ``2`` tensors not commuting, apart with those with ``comm=0`` Other groups can be defined using ``set_comm``; tensors in those groups commute with those with ``comm=0``; by default they do not commute with any other group. """ def __init__(self): self._comm_init() def _comm_init(self): self._comm = [{} for i in range(3)] for i in range(3): self._comm[0][i] = 0 self._comm[i][0] = 0 self._comm[1][1] = 1 self._comm[2][1] = None self._comm[1][2] = None self._comm_symbols2i = {0:0, 1:1, 2:2} self._comm_i2symbol = {0:0, 1:1, 2:2} @property def comm(self): return self._comm
[docs] def comm_symbols2i(self, i): """ get the commutation group number corresponding to ``i`` ``i`` can be a symbol or a number or a string If ``i`` is not already defined its commutation group number is set. """ if i not in self._comm_symbols2i: n = len(self._comm) self._comm.append({}) self._comm[n][0] = 0 self._comm[0][n] = 0 self._comm_symbols2i[i] = n self._comm_i2symbol[n] = i return n return self._comm_symbols2i[i]
[docs] def comm_i2symbol(self, i): """ Returns the symbol corresponding to the commutation group number. """ return self._comm_i2symbol[i]
[docs] def set_comm(self, i, j, c): """ set the commutation parameter ``c`` for commutation groups ``i, j`` Parameters ========== i, j : symbols representing commutation groups c : group commutation number Notes ===== ``i, j`` can be symbols, strings or numbers, apart from ``0, 1`` and ``2`` which are reserved respectively for commuting, anticommuting tensors and tensors not commuting with any other group apart with the commuting tensors. For the remaining cases, use this method to set the commutation rules; by default ``c=None``. The group commutation number ``c`` is assigned in correspondence to the group commutation symbols; it can be 0 commuting 1 anticommuting None no commutation property Examples ======== ``G`` and ``GH`` do not commute with themselves and commute with each other; A is commuting. >>> from sympy.tensor.tensor import TensorIndexType, tensor_indices, tensorhead, TensorManager >>> Lorentz = TensorIndexType('Lorentz') >>> i0,i1,i2,i3,i4 = tensor_indices('i0:5', Lorentz) >>> A = tensorhead('A', [Lorentz], [[1]]) >>> G = tensorhead('G', [Lorentz], [[1]], 'Gcomm') >>> GH = tensorhead('GH', [Lorentz], [[1]], 'GHcomm') >>> TensorManager.set_comm('Gcomm', 'GHcomm', 0) >>> (GH(i1)*G(i0)).canon_bp() G(i0)*GH(i1) >>> (G(i1)*G(i0)).canon_bp() G(i1)*G(i0) >>> (G(i1)*A(i0)).canon_bp() A(i0)*G(i1) """ if c not in (0, 1, None): raise ValueError('`c` can assume only the values 0, 1 or None') if i not in self._comm_symbols2i: n = len(self._comm) self._comm.append({}) self._comm[n][0] = 0 self._comm[0][n] = 0 self._comm_symbols2i[i] = n self._comm_i2symbol[n] = i if j not in self._comm_symbols2i: n = len(self._comm) self._comm.append({}) self._comm[0][n] = 0 self._comm[n][0] = 0 self._comm_symbols2i[j] = n self._comm_i2symbol[n] = j ni = self._comm_symbols2i[i] nj = self._comm_symbols2i[j] self._comm[ni][nj] = c self._comm[nj][ni] = c
[docs] def set_comms(self, *args): """ set the commutation group numbers ``c`` for symbols ``i, j`` Parameters ========== args : sequence of ``(i, j, c)`` """ for i, j, c in args: self.set_comm(i, j, c)
[docs] def get_comm(self, i, j): """ Return the commutation parameter for commutation group numbers ``i, j`` see ``_TensorManager.set_comm`` """ return self._comm[i].get(j, 0 if i == 0 or j == 0 else None)
[docs] def clear(self): """ Clear the TensorManager. """ self._comm_init()
TensorManager = _TensorManager() @doctest_depends_on(modules=('numpy',))
[docs]class TensorIndexType(Basic): """ A TensorIndexType is characterized by its name and its metric. Parameters ========== name : name of the tensor type metric : metric symmetry or metric object or ``None`` dim : dimension, it can be a symbol or an integer or ``None`` eps_dim : dimension of the epsilon tensor dummy_fmt : name of the head of dummy indices Attributes ========== ``name`` ``metric_name`` : it is 'metric' or metric.name ``metric_antisym`` ``metric`` : the metric tensor ``delta`` : ``Kronecker delta`` ``epsilon`` : the ``Levi-Civita epsilon`` tensor ``dim`` ``dim_eps`` ``dummy_fmt`` ``data`` : a property to add ``ndarray`` values, to work in a specified basis. Notes ===== The ``metric`` parameter can be: ``metric = False`` symmetric metric (in Riemannian geometry) ``metric = True`` antisymmetric metric (for spinor calculus) ``metric = None`` there is no metric ``metric`` can be an object having ``name`` and ``antisym`` attributes. If there is a metric the metric is used to raise and lower indices. In the case of antisymmetric metric, the following raising and lowering conventions will be adopted: ``psi(a) = g(a, b)*psi(-b); chi(-a) = chi(b)*g(-b, -a)`` ``g(-a, b) = delta(-a, b); g(b, -a) = -delta(a, -b)`` where ``delta(-a, b) = delta(b, -a)`` is the ``Kronecker delta`` (see ``TensorIndex`` for the conventions on indices). If there is no metric it is not possible to raise or lower indices; e.g. the index of the defining representation of ``SU(N)`` is 'covariant' and the conjugate representation is 'contravariant'; for ``N > 2`` they are linearly independent. ``eps_dim`` is by default equal to ``dim``, if the latter is an integer; else it can be assigned (for use in naive dimensional regularization); if ``eps_dim`` is not an integer ``epsilon`` is ``None``. Examples ======== >>> from sympy.tensor.tensor import TensorIndexType >>> Lorentz = TensorIndexType('Lorentz', dummy_fmt='L') >>> Lorentz.metric metric(Lorentz,Lorentz) Examples with metric components data added, this means it is working on a fixed basis: >>> Lorentz.data = [1, -1, -1, -1] >>> Lorentz TensorIndexType(Lorentz, 0) >>> Lorentz.data [[1 0 0 0] [0 -1 0 0] [0 0 -1 0] [0 0 0 -1]] """ def __new__(cls, name, metric=False, dim=None, eps_dim=None, dummy_fmt=None): if isinstance(name, string_types): name = Symbol(name) obj = Basic.__new__(cls, name, S.One if metric else S.Zero) obj._name = str(name) if not dummy_fmt: obj._dummy_fmt = '%s_%%d' % obj.name else: obj._dummy_fmt = '%s_%%d' % dummy_fmt if metric is None: obj.metric_antisym = None obj.metric = None else: if metric in (True, False, 0, 1): metric_name = 'metric' obj.metric_antisym = metric else: metric_name = metric.name obj.metric_antisym = metric.antisym sym2 = TensorSymmetry(get_symmetric_group_sgs(2, obj.metric_antisym)) S2 = TensorType([obj]*2, sym2) obj.metric = S2(metric_name) obj.metric._matrix_behavior = True obj._dim = dim obj._delta = obj.get_kronecker_delta() obj._eps_dim = eps_dim if eps_dim else dim obj._epsilon = obj.get_epsilon() obj._autogenerated = [] return obj @property def auto_right(self): if not hasattr(self, '_auto_right'): self._auto_right = TensorIndex("auto_right", self) return self._auto_right @property def auto_left(self): if not hasattr(self, '_auto_left'): self._auto_left = TensorIndex("auto_left", self) return self._auto_left @property def auto_index(self): if not hasattr(self, '_auto_index'): self._auto_index = TensorIndex("auto_index", self) return self._auto_index @property def data(self): return _tensor_data_substitution_dict[self] @data.setter def data(self, data): numpy = import_module('numpy') data = _TensorDataLazyEvaluator.parse_data(data) if data.ndim > 2: raise ValueError("data have to be of rank 1 (diagonal metric) or 2.") if data.ndim == 1: if self.dim is not None: nda_dim = data.shape[0] if nda_dim != self.dim: raise ValueError("Dimension mismatch") dim = data.shape[0] newndarray = numpy.zeros((dim, dim), dtype=object) for i, val in enumerate(data): newndarray[i, i] = val data = newndarray dim1, dim2 = data.shape if dim1 != dim2: raise ValueError("Non-square matrix tensor.") if self.dim is not None: if self.dim != dim1: raise ValueError("Dimension mismatch") _tensor_data_substitution_dict[self] = data _tensor_data_substitution_dict.add_metric_data(self.metric, data) delta = self.get_kronecker_delta() i1 = TensorIndex('i1', self) i2 = TensorIndex('i2', self) delta(i1, -i2).data = _TensorDataLazyEvaluator.parse_data(eye(dim1)) @data.deleter def data(self): if self in _tensor_data_substitution_dict: del _tensor_data_substitution_dict[self] if self.metric in _tensor_data_substitution_dict: del _tensor_data_substitution_dict[self.metric] @property def name(self): return self._name @property def dim(self): return self._dim @property def delta(self): return self._delta @property def eps_dim(self): return self._eps_dim @property def epsilon(self): return self._epsilon @property def dummy_fmt(self): return self._dummy_fmt def get_kronecker_delta(self): sym2 = TensorSymmetry(get_symmetric_group_sgs(2)) S2 = TensorType([self]*2, sym2) delta = S2('KD') delta._matrix_behavior = True return delta def get_epsilon(self): if not isinstance(self._eps_dim, int): return None sym = TensorSymmetry(get_symmetric_group_sgs(self._eps_dim, 1)) Sdim = TensorType([self]*self._eps_dim, sym) epsilon = Sdim('Eps') return epsilon def __lt__(self, other): return self.name < other.name def __str__(self): return self.name __repr__ = __str__ def _components_data_full_destroy(self): """ EXPERIMENTAL: do not rely on this API method. This destroys components data associated to the ``TensorIndexType``, if any, specifically: * metric tensor data * Kronecker tensor data """ if self in _tensor_data_substitution_dict: del _tensor_data_substitution_dict[self] def delete_tensmul_data(key): if key in _tensor_data_substitution_dict._substitutions_dict_tensmul: del _tensor_data_substitution_dict._substitutions_dict_tensmul[key] # delete metric data: delete_tensmul_data((self.metric, True, True)) delete_tensmul_data((self.metric, True, False)) delete_tensmul_data((self.metric, False, True)) delete_tensmul_data((self.metric, False, False)) # delete delta tensor data: delta = self.get_kronecker_delta() if delta in _tensor_data_substitution_dict: del _tensor_data_substitution_dict[delta]
@doctest_depends_on(modules=('numpy',))
[docs]class TensorIndex(Basic): """ Represents an abstract tensor index. Parameters ========== name : name of the index, or ``True`` if you want it to be automatically assigned tensortype : ``TensorIndexType`` of the index is_up : flag for contravariant index Attributes ========== ``name`` ``tensortype`` ``is_up`` Notes ===== Tensor indices are contracted with the Einstein summation convention. An index can be in contravariant or in covariant form; in the latter case it is represented prepending a ``-`` to the index name. Dummy indices have a name with head given by ``tensortype._dummy_fmt`` Examples ======== >>> from sympy.tensor.tensor import TensorIndexType, TensorIndex, TensorSymmetry, TensorType, get_symmetric_group_sgs >>> Lorentz = TensorIndexType('Lorentz', dummy_fmt='L') >>> i = TensorIndex('i', Lorentz); i i >>> sym1 = TensorSymmetry(*get_symmetric_group_sgs(1)) >>> S1 = TensorType([Lorentz], sym1) >>> A, B = S1('A,B') >>> A(i)*B(-i) A(L_0)*B(-L_0) If you want the index name to be automatically assigned, just put ``True`` in the ``name`` field, it will be generated using the reserved character ``_`` in front of its name, in order to avoid conflicts with possible existing indices: >>> i0 = TensorIndex(True, Lorentz) >>> i0 _i0 >>> i1 = TensorIndex(True, Lorentz) >>> i1 _i1 >>> A(i0)*B(-i1) A(_i0)*B(-_i1) >>> A(i0)*B(-i0) A(L_0)*B(-L_0) """ def __new__(cls, name, tensortype, is_up=True): if isinstance(name, string_types): name_symbol = Symbol(name) elif isinstance(name, Symbol): name_symbol = name elif name is True: name = "_i{0}".format(len(tensortype._autogenerated)) name_symbol = Symbol(name) tensortype._autogenerated.append(name_symbol) else: raise ValueError("invalid name") obj = Basic.__new__(cls, name_symbol, tensortype, S.One if is_up else S.Zero) obj._name = str(name) obj._tensortype = tensortype obj._is_up = is_up return obj @property def name(self): return self._name @property def tensortype(self): return self._tensortype @property def is_up(self): return self._is_up def _print(self): s = self._name if not self._is_up: s = '-%s' % s return s def __lt__(self, other): return (self._tensortype, self._name) < (other._tensortype, other._name) def __neg__(self): t1 = TensorIndex(self._name, self._tensortype, (not self._is_up)) return t1
[docs]def tensor_indices(s, typ): """ Returns list of tensor indices given their names and their types Parameters ========== s : string of comma separated names of indices typ : list of ``TensorIndexType`` of the indices Examples ======== >>> from sympy.tensor.tensor import TensorIndexType, tensor_indices >>> Lorentz = TensorIndexType('Lorentz', dummy_fmt='L') >>> a, b, c, d = tensor_indices('a,b,c,d', Lorentz) """ if isinstance(s, str): a = [x.name for x in symbols(s, seq=True)] else: raise ValueError('expecting a string') tilist = [TensorIndex(i, typ) for i in a] if len(tilist) == 1: return tilist[0] return tilist
@doctest_depends_on(modules=('numpy',))
[docs]class TensorSymmetry(Basic): """ Monoterm symmetry of a tensor Parameters ========== bsgs : tuple ``(base, sgs)`` BSGS of the symmetry of the tensor Attributes ========== ``base`` : base of the BSGS ``generators`` : generators of the BSGS ``rank`` : rank of the tensor Notes ===== A tensor can have an arbitrary monoterm symmetry provided by its BSGS. Multiterm symmetries, like the cyclic symmetry of the Riemann tensor, are not covered. See Also ======== sympy.combinatorics.tensor_can.get_symmetric_group_sgs Examples ======== Define a symmetric tensor >>> from sympy.tensor.tensor import TensorIndexType, tensor_indices, TensorSymmetry, TensorType, get_symmetric_group_sgs >>> Lorentz = TensorIndexType('Lorentz', dummy_fmt='L') >>> sym2 = TensorSymmetry(get_symmetric_group_sgs(2)) >>> S2 = TensorType([Lorentz]*2, sym2) >>> V = S2('V') """ def __new__(cls, *args, **kw_args): if len(args) == 1: base, generators = args[0] elif len(args) == 2: base, generators = args else: raise TypeError("bsgs required, either two separate parameters or one tuple") if not isinstance(base, Tuple): base = Tuple(*base) if not isinstance(generators, Tuple): generators = Tuple(*generators) obj = Basic.__new__(cls, base, generators, **kw_args) return obj @property def base(self): return self.args[0] @property def generators(self): return self.args[1] @property def rank(self): return self.args[1][0].size - 2
[docs]def tensorsymmetry(*args): """ Return a ``TensorSymmetry`` object. One can represent a tensor with any monoterm slot symmetry group using a BSGS. ``args`` can be a BSGS ``args[0]`` base ``args[1]`` sgs Usually tensors are in (direct products of) representations of the symmetric group; ``args`` can be a list of lists representing the shapes of Young tableaux Notes ===== For instance: ``[[1]]`` vector ``[[1]*n]`` symmetric tensor of rank ``n`` ``[[n]]`` antisymmetric tensor of rank ``n`` ``[[2, 2]]`` monoterm slot symmetry of the Riemann tensor ``[[1],[1]]`` vector*vector ``[[2],[1],[1]`` (antisymmetric tensor)*vector*vector Notice that with the shape ``[2, 2]`` we associate only the monoterm symmetries of the Riemann tensor; this is an abuse of notation, since the shape ``[2, 2]`` corresponds usually to the irreducible representation characterized by the monoterm symmetries and by the cyclic symmetry. Examples ======== Symmetric tensor using a Young tableau >>> from sympy.tensor.tensor import TensorIndexType, TensorType, tensorsymmetry >>> Lorentz = TensorIndexType('Lorentz', dummy_fmt='L') >>> sym2 = tensorsymmetry([1, 1]) >>> S2 = TensorType([Lorentz]*2, sym2) >>> V = S2('V') Symmetric tensor using a ``BSGS`` (base, strong generator set) >>> from sympy.tensor.tensor import TensorSymmetry, get_symmetric_group_sgs >>> sym2 = tensorsymmetry(*get_symmetric_group_sgs(2)) >>> S2 = TensorType([Lorentz]*2, sym2) >>> V = S2('V') """ from sympy.combinatorics import Permutation def tableau2bsgs(a): if len(a) == 1: # antisymmetric vector n = a[0] bsgs = get_symmetric_group_sgs(n, 1) else: if all(x == 1 for x in a): # symmetric vector n = len(a) bsgs = get_symmetric_group_sgs(n) elif a == [2, 2]: bsgs = riemann_bsgs else: raise NotImplementedError return bsgs if not args: return TensorSymmetry(Tuple(), Tuple(Permutation(1))) if len(args) == 2 and isinstance(args[1][0], Permutation): return TensorSymmetry(args) base, sgs = tableau2bsgs(args[0]) for a in args[1:]: basex, sgsx = tableau2bsgs(a) base, sgs = bsgs_direct_product(base, sgs, basex, sgsx) return TensorSymmetry(Tuple(base, sgs))
@doctest_depends_on(modules=('numpy',))
[docs]class TensorType(Basic): """ Class of tensor types. Parameters ========== index_types : list of ``TensorIndexType`` of the tensor indices symmetry : ``TensorSymmetry`` of the tensor Attributes ========== ``index_types`` ``symmetry`` ``types`` : list of ``TensorIndexType`` without repetitions Examples ======== Define a symmetric tensor >>> from sympy.tensor.tensor import TensorIndexType, tensorsymmetry, TensorType >>> Lorentz = TensorIndexType('Lorentz', dummy_fmt='L') >>> sym2 = tensorsymmetry([1, 1]) >>> S2 = TensorType([Lorentz]*2, sym2) >>> V = S2('V') """ is_commutative = False def __new__(cls, index_types, symmetry, **kw_args): assert symmetry.rank == len(index_types) obj = Basic.__new__(cls, Tuple(*index_types), symmetry, **kw_args) return obj @property def index_types(self): return self.args[0] @property def symmetry(self): return self.args[1] @property def types(self): return sorted(set(self.index_types), key=lambda x: x.name) def __str__(self): return 'TensorType(%s)' % ([str(x) for x in self.index_types]) def __call__(self, s, comm=0, matrix_behavior=0): """ Return a TensorHead object or a list of TensorHead objects. ``s`` name or string of names ``comm``: commutation group number see ``_TensorManager.set_comm`` Examples ======== Define symmetric tensors ``V``, ``W`` and ``G``, respectively commuting, anticommuting and with no commutation symmetry >>> from sympy.tensor.tensor import TensorIndexType, tensor_indices, tensorsymmetry, TensorType, canon_bp >>> Lorentz = TensorIndexType('Lorentz', dummy_fmt='L') >>> a, b = tensor_indices('a,b', Lorentz) >>> sym2 = tensorsymmetry([1]*2) >>> S2 = TensorType([Lorentz]*2, sym2) >>> V = S2('V') >>> W = S2('W', 1) >>> G = S2('G', 2) >>> canon_bp(V(a, b)*V(-b, -a)) V(L_0, L_1)*V(-L_0, -L_1) >>> canon_bp(W(a, b)*W(-b, -a)) 0 """ if isinstance(s, str): names = [x.name for x in symbols(s, seq=True)] else: raise ValueError('expecting a string') if len(names) == 1: return TensorHead(names[0], self, comm, matrix_behavior=matrix_behavior) else: return [TensorHead(name, self, comm, matrix_behavior=matrix_behavior) for name in names]
def tensorhead(name, typ, sym, comm=0, matrix_behavior=0): """ Function generating tensorhead(s). Parameters ========== name : name or sequence of names (as in ``symbol``) typ : index types sym : same as ``*args`` in ``tensorsymmetry`` comm : commutation group number see ``_TensorManager.set_comm`` Examples ======== >>> from sympy.tensor.tensor import TensorIndexType, tensor_indices, tensorhead >>> Lorentz = TensorIndexType('Lorentz', dummy_fmt='L') >>> a, b = tensor_indices('a,b', Lorentz) >>> A = tensorhead('A', [Lorentz]*2, [[1]*2]) >>> A(a, -b) A(a, -b) """ sym = tensorsymmetry(*sym) S = TensorType(typ, sym) th = S(name, comm, matrix_behavior=matrix_behavior) return th @doctest_depends_on(modules=('numpy',))
[docs]class TensorHead(Basic): r""" Tensor head of the tensor Parameters ========== name : name of the tensor typ : list of TensorIndexType comm : commutation group number Attributes ========== ``name`` ``index_types`` ``rank`` ``types`` : equal to ``typ.types`` ``symmetry`` : equal to ``typ.symmetry`` ``comm`` : commutation group Notes ===== A ``TensorHead`` belongs to a commutation group, defined by a symbol on number ``comm`` (see ``_TensorManager.set_comm``); tensors in a commutation group have the same commutation properties; by default ``comm`` is ``0``, the group of the commuting tensors. Examples ======== >>> from sympy.tensor.tensor import TensorIndexType, tensorsymmetry, TensorType >>> Lorentz = TensorIndexType('Lorentz', dummy_fmt='L') >>> sym2 = tensorsymmetry([1], [1]) >>> S2 = TensorType([Lorentz]*2, sym2) >>> A = S2('A') Examples with ndarray values, the components data assigned to the ``TensorHead`` object are assumed to be in a fully-contravariant representation. In case it is necessary to assign components data which represents the values of a non-fully covariant tensor, see the other examples. >>> from sympy.tensor.tensor import tensor_indices, tensorhead >>> Lorentz.data = [1, -1, -1, -1] >>> i0, i1 = tensor_indices('i0:2', Lorentz) >>> A.data = [[j+2*i for j in range(4)] for i in range(4)] in order to retrieve data, it is also necessary to specify abstract indices enclosed by round brackets, then numerical indices inside square brackets. >>> A(i0, i1)[0, 0] 0 >>> A(i0, i1)[2, 3] == 3+2*2 True Notice that square brackets create a valued tensor expression instance: >>> A(i0, i1) A(i0, i1) To view the data, just type: >>> A.data [[0 1 2 3] [2 3 4 5] [4 5 6 7] [6 7 8 9]] Turning to a tensor expression, covariant indices get the corresponding components data corrected by the metric: >>> A(i0, -i1).data [[0 -1 -2 -3] [2 -3 -4 -5] [4 -5 -6 -7] [6 -7 -8 -9]] >>> A(-i0, -i1).data [[0 -1 -2 -3] [-2 3 4 5] [-4 5 6 7] [-6 7 8 9]] while if all indices are contravariant, the ``ndarray`` remains the same >>> A(i0, i1).data [[0 1 2 3] [2 3 4 5] [4 5 6 7] [6 7 8 9]] When all indices are contracted and components data are added to the tensor, accessing the data will return a scalar, no numpy object. In fact, numpy ndarrays are dropped to scalars if they contain only one element. >>> A(i0, -i0) A(L_0, -L_0) >>> A(i0, -i0).data -18 It is also possible to assign components data to an indexed tensor, i.e. a tensor with specified covariant and contravariant components. In this example, the covariant components data of the Electromagnetic tensor are injected into `A`: >>> from sympy import symbols >>> Ex, Ey, Ez, Bx, By, Bz = symbols('E_x E_y E_z B_x B_y B_z') >>> c = symbols('c', positive=True) >>> A(-i0, -i1).data = [ ... [0, Ex/c, Ey/c, Ez/c], ... [-Ex/c, 0, -Bz, By], ... [-Ey/c, Bz, 0, -Bx], ... [-Ez/c, -By, Bx, 0]] Now it is possible to retrieve the contravariant form of the Electromagnetic tensor: >>> A(i0, i1).data [[0 -E_x/c -E_y/c -E_z/c] [E_x/c 0 -B_z B_y] [E_y/c B_z 0 -B_x] [E_z/c -B_y B_x 0]] and the mixed contravariant-covariant form: >>> A(i0, -i1).data [[0 E_x/c E_y/c E_z/c] [E_x/c 0 B_z -B_y] [E_y/c -B_z 0 B_x] [E_z/c B_y -B_x 0]] To convert the numpy's ndarray to a sympy matrix, just cast: >>> from sympy import Matrix >>> Matrix(A.data) Matrix([ [ 0, -E_x/c, -E_y/c, -E_z/c], [E_x/c, 0, -B_z, B_y], [E_y/c, B_z, 0, -B_x], [E_z/c, -B_y, B_x, 0]]) Still notice, in this last example, that accessing components data from a tensor without specifying the indices is equivalent to assume that all indices are contravariant. It is also possible to store symbolic components data inside a tensor, for example, define a four-momentum-like tensor: >>> from sympy import symbols >>> P = tensorhead('P', [Lorentz], [[1]]) >>> E, px, py, pz = symbols('E p_x p_y p_z', positive=True) >>> P.data = [E, px, py, pz] The contravariant and covariant components are, respectively: >>> P(i0).data [E p_x p_y p_z] >>> P(-i0).data [E -p_x -p_y -p_z] The contraction of a 1-index tensor by itself is usually indicated by a power by two: >>> P(i0)**2 E**2 - p_x**2 - p_y**2 - p_z**2 As the power by two is clearly identical to `P_\mu P^\mu`, it is possible to simply contract the ``TensorHead`` object, without specifying the indices >>> P**2 E**2 - p_x**2 - p_y**2 - p_z**2 """ is_commutative = False def __new__(cls, name, typ, comm=0, matrix_behavior=0, **kw_args): if isinstance(name, string_types): name_symbol = Symbol(name) elif isinstance(name, Symbol): name_symbol = name else: raise ValueError("invalid name") comm2i = TensorManager.comm_symbols2i(comm) obj = Basic.__new__(cls, name_symbol, typ, **kw_args) obj._matrix_behavior = matrix_behavior obj._name = obj.args[0].name obj._rank = len(obj.index_types) obj._types = typ.types obj._symmetry = typ.symmetry obj._comm = comm2i return obj @property def name(self): return self._name @property def rank(self): return self._rank @property def types(self): return self._types[:] @property def symmetry(self): return self._symmetry @property def typ(self): return self.args[1] @property def comm(self): return self._comm @property def index_types(self): return self.args[1].index_types[:] def __lt__(self, other): return (self.name, self.index_types) < (other.name, other.index_types)
[docs] def commutes_with(self, other): """ Returns ``0`` if ``self`` and ``other`` commute, ``1`` if they anticommute. Returns ``None`` if ``self`` and ``other`` neither commute nor anticommute. """ r = TensorManager.get_comm(self._comm, other._comm) return r
def _print(self): return '%s(%s)' %(self.name, ','.join([str(x) for x in self.index_types])) def _check_auto_matrix_indices_in_call(self, *indices): matrix_behavior_kinds = dict() if len(indices) != len(self.index_types): if not self._matrix_behavior: raise ValueError('wrong number of indices') # _matrix_behavior is True, so take the last one or two missing # indices as auto-matrix indices: ldiff = len(self.index_types) - len(indices) if ldiff > 2: raise ValueError('wrong number of indices') if ldiff == 2: mat_ind = [len(indices), len(indices) + 1] elif ldiff == 1: mat_ind = [len(indices)] not_equal = True else: not_equal = False mat_ind = [i for i, e in enumerate(indices) if e is True] if mat_ind: not_equal = True indices = tuple([_ for _ in indices if _ is not True]) for i, el in enumerate(indices): if not isinstance(el, TensorIndex): not_equal = True break if el._tensortype != self.index_types[i]: not_equal = True break if not_equal: for el in mat_ind: eltyp = self.index_types[el] if eltyp in matrix_behavior_kinds: elind = -self.index_types[el].auto_right matrix_behavior_kinds[eltyp].append(elind) else: elind = self.index_types[el].auto_left matrix_behavior_kinds[eltyp] = [elind] indices = indices[:el] + (elind,) + indices[el:] return indices, matrix_behavior_kinds def __call__(self, *indices): """ Returns a tensor with indices. There is a special behavior in case of indices denoted by ``True``, they are considered auto-matrix indices, their slots are automatically filled, and confer to the tensor the behavior of a matrix or vector upon multiplication with another tensor containing auto-matrix indices of the same ``TensorIndexType``. This means indices get summed over the same way as in matrix multiplication. For matrix behavior, define two auto-matrix indices, for vector behavior define just one. Examples ======== >>> from sympy.tensor.tensor import TensorIndexType, tensor_indices, tensorhead >>> Lorentz = TensorIndexType('Lorentz', dummy_fmt='L') >>> a, b = tensor_indices('a,b', Lorentz) >>> A = tensorhead('A', [Lorentz]*2, [[1]*2]) >>> t = A(a, -b) >>> t A(a, -b) To use the auto-matrix index behavior, just put a ``True`` on the desired index position. >>> r = A(True, True) >>> r A(auto_left, -auto_right) Here ``auto_left`` and ``auto_right`` are automatically generated tensor indices, they are only two for every ``TensorIndexType`` and can be assigned to just one or two indices of a given type. Auto-matrix indices can be assigned many times in a tensor, if indices are of different ``TensorIndexType`` >>> Spinor = TensorIndexType('Spinor', dummy_fmt='S') >>> B = tensorhead('B', [Lorentz, Lorentz, Spinor, Spinor], [[1]*4]) >>> s = B(True, True, True, True) >>> s B(auto_left, -auto_right, auto_left, -auto_right) Here, ``auto_left`` and ``auto_right`` are repeated twice, but they are not the same indices, as they refer to different ``TensorIndexType``s. Auto-matrix indices are automatically contracted upon multiplication, >>> r*s A(auto_left, -L_0)*B(L_0, -auto_right, auto_left, -auto_right) The multiplication algorithm has found an ``auto_right`` index in ``A`` and an ``auto_left`` index in ``B`` referring to the same ``TensorIndexType`` (``Lorentz``), so they have been contracted. Auto-matrix indices can be accessed from the ``TensorIndexType``: >>> Lorentz.auto_right auto_right >>> Lorentz.auto_left auto_left There is a special case, in which the ``True`` parameter is not needed to declare an auto-matrix index, i.e. when the matrix behavior has been declared upon ``TensorHead`` construction, in that case the last one or two tensor indices may be omitted, so that they automatically become auto-matrix indices: >>> C = tensorhead('C', [Lorentz, Lorentz], [[1]*2], matrix_behavior=True) >>> C() C(auto_left, -auto_right) """ indices, matrix_behavior_kinds = self._check_auto_matrix_indices_in_call(*indices) components = [self] tids = TIDS.from_components_and_indices(components, indices) tmul = TensMul.from_TIDS(S.One, tids) tmul._matrix_behavior_kinds = matrix_behavior_kinds return tmul def __pow__(self, other): if self.data is None: raise ValueError("No power on abstract tensors.") numpy = import_module('numpy') metrics = [_.data for _ in self.args[1].args[0]] marray = self.data for metric in metrics: marray = numpy.tensordot(marray, numpy.tensordot(metric, marray, (1, 0)), (0, 0)) pow2 = marray[()] return pow2 ** (Rational(1, 2) * other) @property def data(self): return _tensor_data_substitution_dict[self] @data.setter def data(self, data): _tensor_data_substitution_dict[self] = data @data.deleter def data(self): if self in _tensor_data_substitution_dict: del _tensor_data_substitution_dict[self] def __iter__(self): return self.data.flatten().__iter__() def _components_data_full_destroy(self): """ EXPERIMENTAL: do not rely on this API method. Destroy components data associated to the ``TensorHead`` object, this checks for attached components data, and destroys components data too. """ # do not garbage collect Kronecker tensor (it should be done by # ``TensorIndexType`` garbage collection) if self.name == "KD": return # the data attached to a tensor must be deleted only by the TensorHead # destructor. If the TensorHead is deleted, it means that there are no # more instances of that tensor anywhere. if self in _tensor_data_substitution_dict: del _tensor_data_substitution_dict[self]
@doctest_depends_on(modules=('numpy',))
[docs]class TensExpr(Basic): """ Abstract base class for tensor expressions Notes ===== A tensor expression is an expression formed by tensors; currently the sums of tensors are distributed. A ``TensExpr`` can be a ``TensAdd`` or a ``TensMul``. ``TensAdd`` objects are put in canonical form using the Butler-Portugal algorithm for canonicalization under monoterm symmetries. ``TensMul`` objects are formed by products of component tensors, and include a coefficient, which is a SymPy expression. In the internal representation contracted indices are represented by ``(ipos1, ipos2, icomp1, icomp2)``, where ``icomp1`` is the position of the component tensor with contravariant index, ``ipos1`` is the slot which the index occupies in that component tensor. Contracted indices are therefore nameless in the internal representation. """ _op_priority = 11.0 is_commutative = False def __neg__(self): return self*S.NegativeOne def __abs__(self): raise NotImplementedError def __add__(self, other): raise NotImplementedError def __radd__(self, other): raise NotImplementedError def __sub__(self, other): raise NotImplementedError def __rsub__(self, other): raise NotImplementedError def __mul__(self, other): raise NotImplementedError def __rmul__(self, other): raise NotImplementedError def __pow__(self, other): if self.data is None: raise ValueError("No power without ndarray data.") numpy = import_module('numpy') free = self.free marray = self.data for metric in free: marray = numpy.tensordot( marray, numpy.tensordot( metric[0]._tensortype.data, marray, (1, 0) ), (0, 0) ) pow2 = marray[()] return pow2 ** (Rational(1, 2) * other) def __rpow__(self, other): raise NotImplementedError def __div__(self, other): raise NotImplementedError def __rdiv__(self, other): raise NotImplementedError() __truediv__ = __div__ __rtruediv__ = __rdiv__ @doctest_depends_on(modules=('numpy',))
[docs] def get_matrix(self): """ Returns ndarray components data as a matrix, if components data are available and ndarray dimension does not exceed 2. Examples ======== >>> from sympy.tensor.tensor import TensorIndexType, tensorsymmetry, TensorType >>> from sympy import ones >>> Lorentz = TensorIndexType('Lorentz', dummy_fmt='L') >>> sym2 = tensorsymmetry([1]*2) >>> S2 = TensorType([Lorentz]*2, sym2) >>> A = S2('A') >>> from sympy.tensor.tensor import tensor_indices, tensorhead >>> Lorentz.data = [1, -1, -1, -1] >>> i0, i1 = tensor_indices('i0:2', Lorentz) >>> A.data = [[j+2*i for j in range(4)] for i in range(4)] >>> A(i0, i1).get_matrix() Matrix([ [0, 1, 2, 3], [2, 3, 4, 5], [4, 5, 6, 7], [6, 7, 8, 9]]) It is possible to perform usual operation on matrices, such as the matrix multiplication: >>> A(i0, i1).get_matrix()*ones(4, 1) Matrix([ [ 6], [14], [22], [30]]) """ if 0 < self.rank <= 2: rows = self.data.shape[0] columns = self.data.shape[1] if self.rank == 2 else 1 if self.rank == 2: mat_list = [] * rows for i in range(rows): mat_list.append([]) for j in range(columns): mat_list[i].append(self[i, j]) else: mat_list = [None] * rows for i in range(rows): mat_list[i] = self[i] return Matrix(mat_list) else: raise NotImplementedError( "missing multidimensional reduction to matrix.")
def _eval_simplify(self, ratio, measure): # this is a way to simplify a tensor expression. # This part walks for all `TensorHead`s appearing in the tensor expr # and looks for `simplify_this_type`, to specifically act on a subexpr # containing one type of `TensorHead` instance only: expr = self for i in list(set(self.components)): if hasattr(i, 'simplify_this_type'): expr = i.simplify_this_type(expr) # TODO: missing feature, perform metric contraction. return expr
@doctest_depends_on(modules=('numpy',))
[docs]class TensAdd(TensExpr): """ Sum of tensors Parameters ========== free_args : list of the free indices Attributes ========== ``args`` : tuple of addends ``rank`` : rank of the tensor ``free_args`` : list of the free indices in sorted order Notes ===== Sum of more than one tensor are put automatically in canonical form. Examples ======== >>> from sympy.tensor.tensor import TensorIndexType, tensorhead, tensor_indices >>> Lorentz = TensorIndexType('Lorentz', dummy_fmt='L') >>> a, b = tensor_indices('a,b', Lorentz) >>> p, q = tensorhead('p,q', [Lorentz], [[1]]) >>> t = p(a) + q(a); t p(a) + q(a) >>> t(b) p(b) + q(b) Examples with components data added to the tensor expression: >>> from sympy import eye >>> Lorentz.data = [1, -1, -1, -1] >>> a, b = tensor_indices('a, b', Lorentz) >>> p.data = [2, 3, -2, 7] >>> q.data = [2, 3, -2, 7] >>> t = p(a) + q(a); t p(a) + q(a) >>> t(b) p(b) + q(b) The following are: 2**2 - 3**2 - 2**2 - 7**2 ==> -58 >>> (p(a)*p(-a)).data -58 >>> p(a)**2 -58 """ def __new__(cls, *args, **kw_args): args = [sympify(x) for x in args if x] args = TensAdd._tensAdd_flatten(args) if not args: return S.Zero # replace auto-matrix indices so that they are the same in all addends args = TensAdd._tensAdd_check_automatrix(args) # now check that all addends have the same indices: TensAdd._tensAdd_check(args) args = Tuple(*args) # if TensAdd has only 1 TensMul element in its `args`: if len(args) == 1 and isinstance(args[0], TensMul): obj = Basic.__new__(cls, *args, **kw_args) return obj # canonicalize all TensMul args = [x.canon_bp() for x in args if x] args = [x for x in args if x] # if there are no more args (i.e. have cancelled out), # just return zero: if not args: return S.Zero # collect canonicalized terms args.sort(key=lambda x: (x.components, x.free, x.dum)) a = TensAdd._tensAdd_collect_terms(args) if not a: return S.Zero # it there is only a component tensor return it if len(a) == 1: return a[0] args = Tuple(*args) obj = Basic.__new__(cls, *args, **kw_args) obj._args = tuple(a) return obj @staticmethod def _tensAdd_flatten(args): # flatten TensAdd, coerce terms which are not tensors to tensors if not all(isinstance(x, TensExpr) for x in args): args1 = [] for x in args: if isinstance(x, TensExpr): if isinstance(x, TensAdd): args1.extend(list(x.args)) else: args1.append(x) args1 = [x for x in args1 if isinstance(x, TensExpr) and x._coeff] args2 = [x for x in args if not isinstance(x, TensExpr)] t1 = TensMul.from_data(Add(*args2), [], [], []) args = [t1] + args1 a = [] for x in args: if isinstance(x, TensAdd): a.extend(list(x.args)) else: a.append(x) args = [x for x in a if x._coeff] return args @staticmethod def _tensAdd_check_automatrix(args): # check that all automatrix indices are the same. # if there are no addends, just return. if not args: return args # @type auto_left_types: set auto_left_types = set([]) auto_right_types = set([]) args_auto_left_types = [] args_auto_right_types = [] for i, arg in enumerate(args): arg_auto_left_types = set([]) arg_auto_right_types = set([]) for index in arg.get_indices(): # @type index: TensorIndex if index in (index._tensortype.auto_left, -index._tensortype.auto_left): auto_left_types.add(index._tensortype) arg_auto_left_types.add(index._tensortype) if index in (index._tensortype.auto_right, -index._tensortype.auto_right): auto_right_types.add(index._tensortype) arg_auto_right_types.add(index._tensortype) args_auto_left_types.append(arg_auto_left_types) args_auto_right_types.append(arg_auto_right_types) for arg, aas_left, aas_right in zip(args, args_auto_left_types, args_auto_right_types): missing_left = auto_left_types - aas_left missing_right = auto_right_types - aas_right missing_intersection = missing_left & missing_right for j in missing_intersection: args[i] *= j.delta(j.auto_left, -j.auto_right) if missing_left != missing_right: raise ValueError("cannot determine how to add auto-matrix indices on some args") return args @staticmethod def _tensAdd_check(args): # check that all addends have the same free indices indices0 = set([x[0] for x in args[0].free]) list_indices = [set([y[0] for y in x.free]) for x in args[1:]] if not all(x == indices0 for x in list_indices): raise ValueError('all tensors must have the same indices') @staticmethod def _tensAdd_collect_terms(args): # collect TensMul terms differing at most by their coefficient a = [] prev = args[0] prev_coeff = prev._coeff changed = False for x in args[1:]: # if x and prev have the same tensor, update the coeff of prev if x.components == prev.components \ and x.free == prev.free and x.dum == prev.dum: prev_coeff = prev_coeff + x._coeff changed = True op = 0 else: # x and prev are different; if not changed, prev has not # been updated; store it if not changed: a.append(prev) else: # get a tensor from prev with coeff=prev_coeff and store it if prev_coeff: t = TensMul.from_data(prev_coeff, prev.components, prev.free, prev.dum) a.append(t) # move x to prev op = 1 pprev, prev = prev, x pprev_coeff, prev_coeff = prev_coeff, x._coeff changed = False # if the case op=0 prev was not stored; store it now # in the case op=1 x was not stored; store it now (as prev) if op == 0 and prev_coeff: prev = TensMul.from_data(prev_coeff, prev.components, prev.free, prev.dum) a.append(prev) elif op == 1: a.append(prev) return a @property def rank(self): return self.args[0].rank @property def free_args(self): return self.args[0].free_args def __call__(self, *indices): """Returns tensor with ordered free indices replaced by ``indices`` Parameters ========== indices Examples ======== >>> from sympy import Symbol >>> from sympy.tensor.tensor import TensorIndexType, tensor_indices, tensorhead >>> D = Symbol('D') >>> Lorentz = TensorIndexType('Lorentz', dim=D, dummy_fmt='L') >>> i0,i1,i2,i3,i4 = tensor_indices('i0:5', Lorentz) >>> p, q = tensorhead('p,q', [Lorentz], [[1]]) >>> g = Lorentz.metric >>> t = p(i0)*p(i1) + g(i0,i1)*q(i2)*q(-i2) >>> t(i0,i2) metric(i0, i2)*q(L_0)*q(-L_0) + p(i0)*p(i2) >>> t(i0,i1) - t(i1,i0) 0 """ free_args = self.free_args indices = list(indices) if [x._tensortype for x in indices] != [x._tensortype for x in free_args]: raise ValueError('incompatible types') if indices == free_args: return self index_tuples = list(zip(free_args, indices)) a = [TensMul(*x.fun_eval(*index_tuples).args) for x in self.args] res = TensAdd(*a) return res
[docs] def canon_bp(self): """ canonicalize using the Butler-Portugal algorithm for canonicalization under monoterm symmetries. """ args = [x.canon_bp() for x in self.args] res = TensAdd(*args) return res
def equals(self, other): other = sympify(other) if isinstance(other, TensMul) and other._coeff == 0: return all(x._coeff == 0 for x in self.args) if isinstance(other, TensExpr): if self.rank != other.rank: return False if isinstance(other, TensAdd): if set(self.args) != set(other.args): return False else: return True t = self - other if not isinstance(t, TensExpr): return t == 0 else: if isinstance(t, TensMul): return t._coeff == 0 else: return all(x._coeff == 0 for x in t.args) def __add__(self, other): return TensAdd(self, other) def __radd__(self, other): return TensAdd(other, self) def __sub__(self, other): return TensAdd(self, -other) def __rsub__(self, other): return TensAdd(other, -self) def __mul__(self, other): return TensAdd(*(x*other for x in self.args)) def __rmul__(self, other): return self*other def __div__(self, other): other = sympify(other) if isinstance(other, TensExpr): raise ValueError('cannot divide by a tensor') return TensAdd(*(x/other for x in self.args)) def __rdiv__(self, other): raise ValueError('cannot divide by a tensor') def __getitem__(self, item): return self.data[item] __truediv__ = __div__ __truerdiv__ = __rdiv__ def contract_delta(self, delta): args = [x.contract_delta(delta) for x in self.args] t = TensAdd(*args) return canon_bp(t)
[docs] def contract_metric(self, g): """ Raise or lower indices with the metric ``g`` Parameters ========== g : metric contract_all : if True, eliminate all ``g`` which are contracted Notes ===== see the ``TensorIndexType`` docstring for the contraction conventions """ args = [x.contract_metric(g) for x in self.args] t = TensAdd(*args) return canon_bp(t)
[docs] def fun_eval(self, *index_tuples): """ Return a tensor with free indices substituted according to ``index_tuples`` Parameters ========== index_types : list of tuples ``(old_index, new_index)`` Examples ======== >>> from sympy.tensor.tensor import TensorIndexType, tensor_indices, tensorhead >>> Lorentz = TensorIndexType('Lorentz', dummy_fmt='L') >>> i, j, k, l = tensor_indices('i,j,k,l', Lorentz) >>> A, B = tensorhead('A,B', [Lorentz]*2, [[1]*2]) >>> t = A(i, k)*B(-k, -j) + A(i, -j) >>> t.fun_eval((i, k),(-j, l)) A(k, L_0)*B(l, -L_0) + A(k, l) """ args = self.args args1 = [] for x in args: y = x.fun_eval(*index_tuples) args1.append(y) return TensAdd(*args1)
[docs] def substitute_indices(self, *index_tuples): """ Return a tensor with free indices substituted according to ``index_tuples`` Parameters ========== index_types : list of tuples ``(old_index, new_index)`` Examples ======== >>> from sympy.tensor.tensor import TensorIndexType, tensor_indices, tensorhead >>> Lorentz = TensorIndexType('Lorentz', dummy_fmt='L') >>> i, j, k, l = tensor_indices('i,j,k,l', Lorentz) >>> A, B = tensorhead('A,B', [Lorentz]*2, [[1]*2]) >>> t = A(i, k)*B(-k, -j); t A(i, L_0)*B(-L_0, -j) >>> t.substitute_indices((i,j), (j, k)) A(j, L_0)*B(-L_0, -k) """ args = self.args args1 = [] for x in args: y = x.substitute_indices(*index_tuples) args1.append(y) return TensAdd(*args1)
def _print(self): a = [] args = self.args for x in args: a.append(str(x)) a.sort() s = ' + '.join(a) s = s.replace('+ -', '- ') return s @staticmethod
[docs] def from_TIDS_list(coeff, tids_list): """ Given a list of coefficients and a list of ``TIDS`` objects, construct a ``TensAdd`` instance, equivalent to the one that would result from creating single instances of ``TensMul`` and then adding them. Examples ======== >>> from sympy.tensor.tensor import TensorIndexType, tensor_indices, tensorhead, TensAdd >>> Lorentz = TensorIndexType('Lorentz', dummy_fmt='L') >>> i, j = tensor_indices('i,j', Lorentz) >>> A, B = tensorhead('A,B', [Lorentz]*2, [[1]*2]) >>> eA = 3*A(i, j) >>> eB = 2*B(j, i) >>> t1 = eA._tids >>> t2 = eB._tids >>> c1 = eA.coeff >>> c2 = eB.coeff >>> TensAdd.from_TIDS_list([c1, c2], [t1, t2]) 2*B(i, j) + 3*A(i, j) If the coefficient parameter is a scalar, then it will be applied as a coefficient on all ``TIDS`` objects. >>> TensAdd.from_TIDS_list(4, [t1, t2]) 4*A(i, j) + 4*B(i, j) """ if not isinstance(coeff, (list, tuple, Tuple)): coeff = [coeff] * len(tids_list) tensmul_list = [TensMul.from_TIDS(c, t) for c, t in zip(coeff, tids_list)] return TensAdd(*tensmul_list)
@property def data(self): return _tensor_data_substitution_dict[self] @data.setter def data(self, data): # TODO: check data compatibility with properties of tensor. _tensor_data_substitution_dict[self] = data @data.deleter def data(self): if self in _tensor_data_substitution_dict: del _tensor_data_substitution_dict[self] def __iter__(self): if not self.data: raise ValueError("No iteration on abstract tensors") return self.data.flatten().__iter__()
@doctest_depends_on(modules=('numpy',))
[docs]class TensMul(TensExpr): """ Product of tensors Parameters ========== coeff : SymPy coefficient of the tensor args Attributes ========== ``components`` : list of ``TensorHead`` of the component tensors ``types`` : list of nonrepeated ``TensorIndexType`` ``free`` : list of ``(ind, ipos, icomp)``, see Notes ``dum`` : list of ``(ipos1, ipos2, icomp1, icomp2)``, see Notes ``ext_rank`` : rank of the tensor counting the dummy indices ``rank`` : rank of the tensor ``coeff`` : SymPy coefficient of the tensor ``free_args`` : list of the free indices in sorted order ``is_canon_bp`` : ``True`` if the tensor in in canonical form Notes ===== ``args[0]`` list of ``TensorHead`` of the component tensors. ``args[1]`` list of ``(ind, ipos, icomp)`` where ``ind`` is a free index, ``ipos`` is the slot position of ``ind`` in the ``icomp``-th component tensor. ``args[2]`` list of tuples representing dummy indices. ``(ipos1, ipos2, icomp1, icomp2)`` indicates that the contravariant dummy index is the ``ipos1``-th slot position in the ``icomp1``-th component tensor; the corresponding covariant index is in the ``ipos2`` slot position in the ``icomp2``-th component tensor. """ def __new__(cls, coeff, *args, **kw_args): coeff = sympify(coeff) if len(args) == 2: components = args[0] indices = args[1] tids = TIDS.from_components_and_indices(components, indices) elif len(args) == 1: tids = args[0] components = tids.components indices = tids.to_indices() else: raise TypeError("wrong construction") for i in indices: if not isinstance(i, TensorIndex): raise TypeError("i should be of type TensorIndex") t_components = Tuple(*components) t_indices = Tuple(*indices) obj = Basic.__new__(cls, coeff, t_components, t_indices) obj._types = [] for t in tids.components: obj._types.extend(t._types) obj._tids = tids obj._ext_rank = len(obj._tids.free) + 2*len(obj._tids.dum) obj._coeff = coeff obj._is_canon_bp = kw_args.get('is_canon_bp', False) obj._matrix_behavior_kinds = dict() return obj @staticmethod def from_data(coeff, components, free, dum, **kw_args): tids = TIDS(components, free, dum) return TensMul.from_TIDS(coeff, tids, **kw_args) @staticmethod def from_TIDS(coeff, tids, **kw_args): return TensMul(coeff, tids, **kw_args) @property def free_args(self): return sorted([x[0] for x in self.free]) @property def components(self): return self._tids.components[:] @property def free(self): return self._tids.free[:] @property def coeff(self): return self._coeff @property def dum(self): return self._tids.dum[:] @property def rank(self): return len(self.free) @property def types(self): return self._types[:] def equals(self, other): if other == 0: return self.coeff == 0 other = sympify(other) if not isinstance(other, TensExpr): assert not self.components return self._coeff == other def _get_compar_comp(self): t = self.canon_bp() r = (t._coeff, tuple(t.components), \ tuple(sorted(t.free)), tuple(sorted(t.dum))) return r return _get_compar_comp(self) == _get_compar_comp(other)
[docs] def get_indices(self): """ Returns the list of indices of the tensor The indices are listed in the order in which they appear in the component tensors. The dummy indices are given a name which does not collide with the names of the free indices. Examples ======== >>> from sympy.tensor.tensor import TensorIndexType, tensor_indices, tensorhead >>> Lorentz = TensorIndexType('Lorentz', dummy_fmt='L') >>> m0, m1, m2 = tensor_indices('m0,m1,m2', Lorentz) >>> g = Lorentz.metric >>> p, q = tensorhead('p,q', [Lorentz], [[1]]) >>> t = p(m1)*g(m0,m2) >>> t.get_indices() [m1, m0, m2] """ indices = [None]*self._ext_rank start = 0 pos = 0 vpos = [] components = self.components for t in components: vpos.append(pos) pos += t._rank cdt = defaultdict(int) # if the free indices have names with dummy_fmt, start with an # index higher than those for the dummy indices # to avoid name collisions for indx, ipos, cpos in self.free: if indx._name.split('_')[0] == indx._tensortype._dummy_fmt[:-3]: cdt[indx._tensortype] = max(cdt[indx._tensortype], int(indx._name.split('_')[1]) + 1) start = vpos[cpos] indices[start + ipos] = indx for ipos1, ipos2, cpos1, cpos2 in self.dum: start1 = vpos[cpos1] start2 = vpos[cpos2] typ1 = components[cpos1].index_types[ipos1] assert typ1 == components[cpos2].index_types[ipos2] fmt = typ1._dummy_fmt nd = cdt[typ1] indices[start1 + ipos1] = TensorIndex(fmt % nd, typ1) indices[start2 + ipos2] = TensorIndex(fmt % nd, typ1, False) cdt[typ1] += 1 return indices
[docs] def split(self): """ Returns a list of tensors, whose product is ``self`` Dummy indices contracted among different tensor components become free indices with the same name as the one used to represent the dummy indices. Examples ======== >>> from sympy.tensor.tensor import TensorIndexType, tensor_indices, tensorhead >>> Lorentz = TensorIndexType('Lorentz', dummy_fmt='L') >>> a, b, c, d = tensor_indices('a,b,c,d', Lorentz) >>> A, B = tensorhead('A,B', [Lorentz]*2, [[1]*2]) >>> t = A(a,b)*B(-b,c) >>> t A(a, L_0)*B(-L_0, c) >>> t.split() [A(a, L_0), B(-L_0, c)] """ indices = self.get_indices() pos = 0 components = self.components if not components: return [TensMul.from_data(self._coeff, [], [], [])] res = [] for t in components: t1 = t(*indices[pos:pos + t._rank]) pos += t._rank res.append(t1) res[0] = TensMul.from_data(self._coeff, res[0].components, res[0]._tids.free, res[0]._tids.dum, is_canon_bp=res[0]._is_canon_bp) return res
def __add__(self, other): return TensAdd(self, other) def __radd__(self, other): return TensAdd(other, self) def __sub__(self, other): return TensAdd(self, -other) def __rsub__(self, other): return TensAdd(other, -self) def __mul__(self, other): """ Multiply two tensors using Einstein summation convention. If the two tensors have an index in common, one contravariant and the other covariant, in their product the indices are summed Examples ======== >>> from sympy.tensor.tensor import TensorIndexType, tensor_indices, tensorhead >>> Lorentz = TensorIndexType('Lorentz', dummy_fmt='L') >>> m0, m1, m2 = tensor_indices('m0,m1,m2', Lorentz) >>> g = Lorentz.metric >>> p, q = tensorhead('p,q', [Lorentz], [[1]]) >>> t1 = p(m0) >>> t2 = q(-m0) >>> t1*t2 p(L_0)*q(-L_0) """ other = sympify(other) if not isinstance(other, TensExpr): coeff = self._coeff*other tmul = TensMul.from_TIDS(coeff, self._tids, is_canon_bp=self._is_canon_bp) tmul._matrix_behavior_kinds = self._matrix_behavior_kinds return tmul if isinstance(other, TensAdd): return TensAdd(*[self*x for x in other.args]) matrix_behavior_kinds = dict() self_matrix_behavior_kinds = self._matrix_behavior_kinds other_matrix_behavior_kinds = other._matrix_behavior_kinds for key, v1 in self_matrix_behavior_kinds.items(): if key in other_matrix_behavior_kinds: v2 = other_matrix_behavior_kinds[key] if len(v1) == 1: other = other.substitute_indices((v2[0], -v1[0])) if len(v2) == 2: matrix_behavior_kinds[key] = (v2[1],) elif len(v1) == 2: auto_index = v1[1]._tensortype.auto_index self = self.substitute_indices((v1[1], -auto_index)) other = other.substitute_indices((v2[0], auto_index)) if len(v2) == 1: matrix_behavior_kinds[key] = (v1[0],) elif len(v2) == 2: matrix_behavior_kinds[key] = (v1[0], v2[1]) else: matrix_behavior_kinds[key] = v1 for key, v2 in other_matrix_behavior_kinds.items(): if key in self_matrix_behavior_kinds: continue matrix_behavior_kinds[key] = v2 new_tids = self._tids*other._tids coeff = self._coeff*other._coeff tmul = TensMul.from_TIDS(coeff, new_tids) if isinstance(tmul, TensExpr): tmul._matrix_behavior_kinds = matrix_behavior_kinds return tmul def __rmul__(self, other): other = sympify(other) coeff = other*self._coeff tmul = TensMul.from_TIDS(coeff, self._tids) tmul._matrix_behavior_kinds = self._matrix_behavior_kinds return tmul def __div__(self, other): other = sympify(other) if isinstance(other, TensExpr): raise ValueError('cannot divide by a tensor') coeff = self._coeff/other tmul = TensMul.from_TIDS(coeff, self._tids, is_canon_bp=self._is_canon_bp) tmul._matrix_behavior_kinds = self._matrix_behavior_kinds return tmul def __rdiv__(self, other): raise ValueError('cannot divide by a tensor') def __getitem__(self, item): return self.data[item] __truediv__ = __div__ __truerdiv__ = __rdiv__
[docs] def sorted_components(self): """ Returns a tensor with sorted components calling the corresponding method in a ``TIDS`` object. """ new_tids, sign = self._tids.sorted_components() coeff = -self._coeff if sign == -1 else self._coeff t = TensMul.from_TIDS(coeff, new_tids) return t
[docs] def perm2tensor(self, g, canon_bp=False): """ Returns the tensor corresponding to the permutation ``g`` For further details, see the method in ``TIDS`` with the same name. """ new_tids = self._tids.perm2tensor(g, canon_bp) coeff = self._coeff if g[-1] != len(g) - 1: coeff = -coeff res = TensMul.from_TIDS(coeff, new_tids, is_canon_bp=canon_bp) res._matrix_behavior_kinds = self._matrix_behavior_kinds return res
[docs] def canon_bp(self): """ Canonicalize using the Butler-Portugal algorithm for canonicalization under monoterm symmetries. Examples ======== >>> from sympy.tensor.tensor import TensorIndexType, tensor_indices, tensorhead >>> Lorentz = TensorIndexType('Lorentz', dummy_fmt='L') >>> m0, m1, m2 = tensor_indices('m0,m1,m2', Lorentz) >>> A = tensorhead('A', [Lorentz]*2, [[2]]) >>> t = A(m0,-m1)*A(m1,-m0) >>> t.canon_bp() -A(L_0, L_1)*A(-L_0, -L_1) >>> t = A(m0,-m1)*A(m1,-m2)*A(m2,-m0) >>> t.canon_bp() 0 """ if self._is_canon_bp: return self if not self.components: return self t = self.sorted_components() g, dummies, msym, v = t._tids.canon_args() can = canonicalize(g, dummies, msym, *v) if can == 0: return S.Zero tmul = t.perm2tensor(can, True) tmul._matrix_behavior_kinds = self._matrix_behavior_kinds return tmul
def contract_delta(self, delta): t = self.contract_metric(delta) return t
[docs] def contract_metric(self, g): """ Raise or lower indices with the metric ``g`` Parameters ========== g : metric Notes ===== see the ``TensorIndexType`` docstring for the contraction conventions Examples ======== >>> from sympy.tensor.tensor import TensorIndexType, tensor_indices, tensorhead >>> Lorentz = TensorIndexType('Lorentz', dummy_fmt='L') >>> m0, m1, m2 = tensor_indices('m0,m1,m2', Lorentz) >>> g = Lorentz.metric >>> p, q = tensorhead('p,q', [Lorentz], [[1]]) >>> t = p(m0)*q(m1)*g(-m0, -m1) >>> t.canon_bp() metric(L_0, L_1)*p(-L_0)*q(-L_1) >>> t.contract_metric(g).canon_bp() p(L_0)*q(-L_0) """ components = self.components antisym = g.index_types[0].metric_antisym #if not any(x == g for x in components): # return self # list of positions of the metric ``g`` gpos = [i for i, x in enumerate(components) if x == g] if not gpos: return self coeff = self._coeff tids = self._tids dum = tids.dum[:] free = tids.free[:] elim = set() for gposx in gpos: if gposx in elim: continue free1 = [x for x in free if x[-1] == gposx] dum1 = [x for x in dum if x[-2] == gposx or x[-1] == gposx] if not dum1: continue elim.add(gposx) if len(dum1) == 2: if not antisym: dum10, dum11 = dum1 if dum10[3] == gposx: # the index with pos p0 and component c0 is contravariant c0 = dum10[2] p0 = dum10[0] else: # the index with pos p0 and component c0 is covariant c0 = dum10[3] p0 = dum10[1] if dum11[3] == gposx: # the index with pos p1 and component c1 is contravariant c1 = dum11[2] p1 = dum11[0] else: # the index with pos p1 and component c1 is covariant c1 = dum11[3] p1 = dum11[1] dum.append((p0, p1, c0, c1)) else: dum10, dum11 = dum1 # change the sign to bring the indices of the metric to contravariant # form; change the sign if dum10 has the metric index in position 0 if dum10[3] == gposx: # the index with pos p0 and component c0 is contravariant c0 = dum10[2] p0 = dum10[0] if dum10[1] == 1: coeff = -coeff else: # the index with pos p0 and component c0 is covariant c0 = dum10[3] p0 = dum10[1] if dum10[0] == 0: coeff = -coeff if dum11[3] == gposx: # the index with pos p1 and component c1 is contravariant c1 = dum11[2] p1 = dum11[0] coeff = -coeff else: # the index with pos p1 and component c1 is covariant c1 = dum11[3] p1 = dum11[1] dum.append((p0, p1, c0, c1)) elif len(dum1) == 1: if not antisym: dp0, dp1, dc0, dc1 = dum1[0] if dc0 == dc1: # g(i, -i) typ = g.index_types[0] if typ._dim is None: raise ValueError('dimension not assigned') coeff = coeff*typ._dim else: # g(i0, i1)*p(-i1) if dc0 == gposx: p1 = dp1 c1 = dc1 else: p1 = dp0 c1 = dc0 ind, p, c = free1[0] free.append((ind, p1, c1)) else: dp0, dp1, dc0, dc1 = dum1[0] if dc0 == dc1: # g(i, -i) typ = g.index_types[0] if typ._dim is None: raise ValueError('dimension not assigned') coeff = coeff*typ._dim if dp0 < dp1: # g(i, -i) = -D with antisymmetric metric coeff = -coeff else: # g(i0, i1)*p(-i1) if dc0 == gposx: p1 = dp1 c1 = dc1 if dp0 == 0: coeff = -coeff else: p1 = dp0 c1 = dc0 ind, p, c = free1[0] free.append((ind, p1, c1)) dum = [x for x in dum if x not in dum1] free = [x for x in free if x not in free1] shift = 0 shifts = [0]*len(components) for i in range(len(components)): if i in elim: shift += 1 continue shifts[i] = shift free = [(ind, p, c - shifts[c]) for (ind, p, c) in free if c not in elim] dum = [(p0, p1, c0 - shifts[c0], c1 - shifts[c1]) for i, (p0, p1, c0, c1) in enumerate(dum) if c0 not in elim and c1 not in elim] components = [c for i, c in enumerate(components) if i not in elim] tids = TIDS(components, free, dum) res = TensMul.from_TIDS(coeff, tids) return res
[docs] def substitute_indices(self, *index_tuples): """ Return a tensor with free indices substituted according to ``index_tuples`` ``index_types`` list of tuples ``(old_index, new_index)`` Note: this method will neither raise or lower the indices, it will just replace their symbol. Examples ======== >>> from sympy.tensor.tensor import TensorIndexType, tensor_indices, tensorhead >>> Lorentz = TensorIndexType('Lorentz', dummy_fmt='L') >>> i, j, k, l = tensor_indices('i,j,k,l', Lorentz) >>> A, B = tensorhead('A,B', [Lorentz]*2, [[1]*2]) >>> t = A(i, k)*B(-k, -j); t A(i, L_0)*B(-L_0, -j) >>> t.substitute_indices((i,j), (j, k)) A(j, L_0)*B(-L_0, -k) """ free = self.free free1 = [] for j, ipos, cpos in free: for i, v in index_tuples: if i._name == j._name and i._tensortype == j._tensortype: if i._is_up == j._is_up: free1.append((v, ipos, cpos)) else: free1.append((-v, ipos, cpos)) break else: free1.append((j, ipos, cpos)) t = TensMul.from_data(self._coeff, self.components, free1, self.dum) # object is rebuilt in order to make sure that all contracted indices get recognized as dummies. # t2 = TensMul(*t.args) return t
[docs] def fun_eval(self, *index_tuples): """ Return a tensor with free indices substituted according to ``index_tuples`` ``index_types`` list of tuples ``(old_index, new_index)`` Examples ======== >>> from sympy.tensor.tensor import TensorIndexType, tensor_indices, tensorhead >>> Lorentz = TensorIndexType('Lorentz', dummy_fmt='L') >>> i, j, k, l = tensor_indices('i,j,k,l', Lorentz) >>> A, B = tensorhead('A,B', [Lorentz]*2, [[1]*2]) >>> t = A(i, k)*B(-k, -j); t A(i, L_0)*B(-L_0, -j) >>> t.fun_eval((i, k),(-j, l)) A(k, L_0)*B(-L_0, l) """ free = self.free free1 = [] for j, ipos, cpos in free: # search j in index_tuples for i, v in index_tuples: if i == j: free1.append((v, ipos, cpos)) break else: free1.append((j, ipos, cpos)) return TensMul.from_data(self._coeff, self.components, free1, self.dum)
def __call__(self, *indices): """Returns tensor with ordered free indices replaced by ``indices`` Examples ======== >>> from sympy import Symbol >>> from sympy.tensor.tensor import TensorIndexType, tensor_indices, tensorhead >>> D = Symbol('D') >>> Lorentz = TensorIndexType('Lorentz', dim=D, dummy_fmt='L') >>> i0,i1,i2,i3,i4 = tensor_indices('i0:5', Lorentz) >>> g = Lorentz.metric >>> p, q = tensorhead('p,q', [Lorentz], [[1]]) >>> t = p(i0)*q(i1)*q(-i1) >>> t(i1) p(i1)*q(L_0)*q(-L_0) """ free_args = self.free_args indices = list(indices) if [x._tensortype for x in indices] != [x._tensortype for x in free_args]: raise ValueError('incompatible types') if indices == free_args: return self t = self.fun_eval(*list(zip(free_args, indices))) # object is rebuilt in order to make sure that all contracted indices # get recognized as dummies, but only if there are contracted indices. if len(set(i if i.is_up else -i for i in indices)) != len(indices): return t.func(*t.args) return t def _print(self): if len(self.components) == 0: return str(self._coeff) indices = [str(ind) for ind in self.get_indices()] pos = 0 a = [] for t in self.components: if t._rank > 0: a.append('%s(%s)' % (t.name, ', '.join(indices[pos:pos + t._rank]))) else: a.append('%s' % t.name) pos += t._rank res = '*'. join(a) if self._coeff == S.One: return res elif self._coeff == -S.One: return '-%s' % res if self._coeff.is_Atom: return '%s*%s' % (self._coeff, res) else: return '(%s)*%s' %(self._coeff, res) @property def data(self): dat = _tensor_data_substitution_dict[self] if dat is None: return None return self.coeff * dat @data.setter def data(self, data): # TODO: check data compatibility with properties of tensor. _tensor_data_substitution_dict[self] = data @data.deleter def data(self): if self in _tensor_data_substitution_dict: del _tensor_data_substitution_dict[self] def __iter__(self): if self.data is None: raise ValueError("No iteration on abstract tensors") return (self.data.flatten()).__iter__()
[docs]def canon_bp(p): """ Butler-Portugal canonicalization """ if isinstance(p, TensExpr): return p.canon_bp() return p
[docs]def tensor_mul(*a): """ product of tensors """ if not a: return TensMul.from_data(S.One, [], [], []) t = a[0] for tx in a[1:]: t = t*tx return t
[docs]def riemann_cyclic_replace(t_r): """ replace Riemann tensor with an equivalent expression ``R(m,n,p,q) -> 2/3*R(m,n,p,q) - 1/3*R(m,q,n,p) + 1/3*R(m,p,n,q)`` """ free = sorted(t_r.free, key=lambda x: x[1]) m, n, p, q = [x[0] for x in free] t0 = S(2)/3*t_r t1 = - S(1)/3*t_r.substitute_indices((m,m),(n,q),(p,n),(q,p)) t2 = S(1)/3*t_r.substitute_indices((m,m),(n,p),(p,n),(q,q)) t3 = t0 + t1 + t2 return t3
[docs]def riemann_cyclic(t2): """ replace each Riemann tensor with an equivalent expression satisfying the cyclic identity. This trick is discussed in the reference guide to Cadabra. Examples ======== >>> from sympy.tensor.tensor import TensorIndexType, tensor_indices, tensorhead, riemann_cyclic >>> Lorentz = TensorIndexType('Lorentz', dummy_fmt='L') >>> i, j, k, l = tensor_indices('i,j,k,l', Lorentz) >>> R = tensorhead('R', [Lorentz]*4, [[2, 2]]) >>> t = R(i,j,k,l)*(R(-i,-j,-k,-l) - 2*R(-i,-k,-j,-l)) >>> riemann_cyclic(t) 0 """ if isinstance(t2, TensMul): args = [t2] else: args = t2.args a1 = [x.split() for x in args] a2 = [[riemann_cyclic_replace(tx) for tx in y] for y in a1] a3 = [tensor_mul(*v) for v in a2] t3 = TensAdd(*a3) if not t3: return t3 else: return canon_bp(t3)
def get_lines(ex, index_type): """ returns ``(lines, traces, rest)`` for an index type, where ``lines`` is the list of list of positions of a matrix line, ``traces`` is the list of list of traced matrix lines, ``rest`` is the rest of the elements ot the tensor. """ def _join_lines(a): i = 0 while i < len(a): x = a[i] xend = x[-1] hit = True while hit: hit = False for j in range(i + 1, len(a)): if j >= len(a): break if a[j][0] == xend: hit = True x.extend(a[j][1:]) xend = x[-1] a.pop(j) i += 1 return a tids = ex._tids components = tids.components dt = {} for c in components: if c in dt: continue index_types = c.index_types a = [] for i in range(len(index_types)): if index_types[i] is index_type: a.append(i) if len(a) > 2: raise ValueError('at most two indices of type %s allowed' % index_type) if len(a) == 2: dt[c] = a dum = tids.dum lines = [] traces = [] traces1 = [] for p0, p1, c0, c1 in dum: if components[c0] not in dt: continue if c0 == c1: traces.append([c0]) continue ta0 = dt[components[c0]] ta1 = dt[components[c1]] if p0 not in ta0: continue if ta0.index(p0) == ta1.index(p1): # case gamma(i,s0,-s1)in c0, gamma(j,-s0,s2) in c1; # to deal with this case one could add to the position # a flag for transposition; # one could write [(c0, False), (c1, True)] raise NotImplementedError # if p0 == ta0[1] then G in pos c0 is mult on the right by G in c1 # if p0 == ta0[0] then G in pos c1 is mult on the right by G in c0 ta0 = dt[components[c0]] b0, b1 = (c0, c1) if p0 == ta0[1] else (c1, c0) lines1 = lines[:] for line in lines: if line[-1] == b0: if line[0] == b1: n = line.index(min(line)) traces1.append(line) traces.append(line[n:] + line[:n]) else: line.append(b1) break elif line[0] == b1: line.insert(0, b0) break else: lines1.append([b0, b1]) lines = [x for x in lines1 if x not in traces1] lines = _join_lines(lines) rest = [] for line in lines: for y in line: rest.append(y) for line in traces: for y in line: rest.append(y) rest = [x for x in range(len(components)) if x not in rest] return lines, traces, rest