Source code for sympy.tensor.array.arrayop

import itertools

import collections

from sympy import S, Tuple, diff

from sympy.tensor.array import ImmutableDenseNDimArray
from sympy.tensor.array.ndim_array import NDimArray


def _arrayfy(a):
    from sympy.matrices import MatrixBase

    if isinstance(a, NDimArray):
        return a
    if isinstance(a, (MatrixBase, list, tuple, Tuple)):
        return ImmutableDenseNDimArray(a)
    return a


[docs]def tensorproduct(*args): """ Tensor product among scalars or array-like objects. Examples ======== >>> from sympy.tensor.array import tensorproduct, Array >>> from sympy.abc import x, y, z, t >>> A = Array([[1, 2], [3, 4]]) >>> B = Array([x, y]) >>> tensorproduct(A, B) [[[x, y], [2*x, 2*y]], [[3*x, 3*y], [4*x, 4*y]]] >>> tensorproduct(A, x) [[x, 2*x], [3*x, 4*x]] >>> tensorproduct(A, B, B) [[[[x**2, x*y], [x*y, y**2]], [[2*x**2, 2*x*y], [2*x*y, 2*y**2]]], [[[3*x**2, 3*x*y], [3*x*y, 3*y**2]], [[4*x**2, 4*x*y], [4*x*y, 4*y**2]]]] Applying this function on two matrices will result in a rank 4 array. >>> from sympy import Matrix, eye >>> m = Matrix([[x, y], [z, t]]) >>> p = tensorproduct(eye(3), m) >>> p [[[[x, y], [z, t]], [[0, 0], [0, 0]], [[0, 0], [0, 0]]], [[[0, 0], [0, 0]], [[x, y], [z, t]], [[0, 0], [0, 0]]], [[[0, 0], [0, 0]], [[0, 0], [0, 0]], [[x, y], [z, t]]]] """ if len(args) == 0: return S.One if len(args) == 1: return _arrayfy(args[0]) if len(args) > 2: return tensorproduct(tensorproduct(args[0], args[1]), *args[2:]) # length of args is 2: a, b = map(_arrayfy, args) if not isinstance(a, NDimArray) or not isinstance(b, NDimArray): return a*b al = list(a) bl = list(b) product_list = [i*j for i in al for j in bl] return ImmutableDenseNDimArray(product_list, a.shape + b.shape)
[docs]def tensorcontraction(array, *contraction_axes): """ Contraction of an array-like object on the specified axes. Examples ======== >>> from sympy import Array, tensorcontraction >>> from sympy import Matrix, eye >>> tensorcontraction(eye(3), (0, 1)) 3 >>> A = Array(range(18), (3, 2, 3)) >>> A [[[0, 1, 2], [3, 4, 5]], [[6, 7, 8], [9, 10, 11]], [[12, 13, 14], [15, 16, 17]]] >>> tensorcontraction(A, (0, 2)) [21, 30] Matrix multiplication may be emulated with a proper combination of ``tensorcontraction`` and ``tensorproduct`` >>> from sympy import tensorproduct >>> from sympy.abc import a,b,c,d,e,f,g,h >>> m1 = Matrix([[a, b], [c, d]]) >>> m2 = Matrix([[e, f], [g, h]]) >>> p = tensorproduct(m1, m2) >>> p [[[[a*e, a*f], [a*g, a*h]], [[b*e, b*f], [b*g, b*h]]], [[[c*e, c*f], [c*g, c*h]], [[d*e, d*f], [d*g, d*h]]]] >>> tensorcontraction(p, (1, 2)) [[a*e + b*g, a*f + b*h], [c*e + d*g, c*f + d*h]] >>> m1*m2 Matrix([ [a*e + b*g, a*f + b*h], [c*e + d*g, c*f + d*h]]) """ array = _arrayfy(array) # Verify contraction_axes: taken_dims = set([]) for axes_group in contraction_axes: if not isinstance(axes_group, collections.Iterable): raise ValueError("collections of contraction axes expected") dim = array.shape[axes_group[0]] for d in axes_group: if d in taken_dims: raise ValueError("dimension specified more than once") if dim != array.shape[d]: raise ValueError("cannot contract between axes of different dimension") taken_dims.add(d) rank = array.rank() remaining_shape = [dim for i, dim in enumerate(array.shape) if i not in taken_dims] cum_shape = [0]*rank _cumul = 1 for i in range(rank): cum_shape[rank - i - 1] = _cumul _cumul *= int(array.shape[rank - i - 1]) # DEFINITION: by absolute position it is meant the position along the one # dimensional array containing all the tensor components. # Possible future work on this module: move computation of absolute # positions to a class method. # Determine absolute positions of the uncontracted indices: remaining_indices = [[cum_shape[i]*j for j in range(array.shape[i])] for i in range(rank) if i not in taken_dims] # Determine absolute positions of the contracted indices: summed_deltas = [] for axes_group in contraction_axes: lidx = [] for js in range(array.shape[axes_group[0]]): lidx.append(sum([cum_shape[ig] * js for ig in axes_group])) summed_deltas.append(lidx) # Compute the contracted array: # # 1. external for loops on all uncontracted indices. # Uncontracted indices are determined by the combinatorial product of # the absolute positions of the remaining indices. # 2. internal loop on all contracted indices. # It sum the values of the absolute contracted index and the absolute # uncontracted index for the external loop. contracted_array = [] for icontrib in itertools.product(*remaining_indices): index_base_position = sum(icontrib) isum = S.Zero for sum_to_index in itertools.product(*summed_deltas): isum += array[index_base_position + sum(sum_to_index)] contracted_array.append(isum) if len(remaining_indices) == 0: assert len(contracted_array) == 1 return contracted_array[0] return type(array)(contracted_array, remaining_shape)
[docs]def derive_by_array(expr, dx): r""" Derivative by arrays. Supports both arrays and scalars. Given the array `A_{i_1, \ldots, i_N}` and the array `X_{j_1, \ldots, j_M}` this function will return a new array `B` defined by `B_{j_1,\ldots,j_M,i_1,\ldots,i_N} := \frac{\partial A_{i_1,\ldots,i_N}}{\partial X_{j_1,\ldots,j_M}}` Examples ======== >>> from sympy import derive_by_array >>> from sympy.abc import x, y, z, t >>> from sympy import cos >>> derive_by_array(cos(x*t), x) -t*sin(t*x) >>> derive_by_array(cos(x*t), [x, y, z, t]) [-t*sin(t*x), 0, 0, -x*sin(t*x)] >>> derive_by_array([x, y**2*z], [[x, y], [z, t]]) [[[1, 0], [0, 2*y*z]], [[0, y**2], [0, 0]]] """ from sympy.matrices import MatrixBase array_types = (collections.Iterable, MatrixBase, NDimArray) if isinstance(dx, array_types): dx = ImmutableDenseNDimArray(dx) for i in dx: if not i._diff_wrt: raise ValueError("cannot derive by this array") if isinstance(expr, array_types): expr = ImmutableDenseNDimArray(expr) if isinstance(dx, array_types): new_array = [[y.diff(x) for y in expr] for x in dx] return type(expr)(new_array, dx.shape + expr.shape) else: return expr.diff(dx) else: if isinstance(dx, array_types): return ImmutableDenseNDimArray([expr.diff(i) for i in dx], dx.shape) else: return diff(expr, dx)
[docs]def permutedims(expr, perm): """ Permutes the indices of an array. Parameter specifies the permutation of the indices. Examples ======== >>> from sympy.abc import x, y, z, t >>> from sympy import sin >>> from sympy import Array, permutedims >>> a = Array([[x, y, z], [t, sin(x), 0]]) >>> a [[x, y, z], [t, sin(x), 0]] >>> permutedims(a, (1, 0)) [[x, t], [y, sin(x)], [z, 0]] If the array is of second order, ``transpose`` can be used: >>> from sympy import transpose >>> transpose(a) [[x, t], [y, sin(x)], [z, 0]] Examples on higher dimensions: >>> b = Array([[[1, 2], [3, 4]], [[5, 6], [7, 8]]]) >>> permutedims(b, (2, 1, 0)) [[[1, 5], [3, 7]], [[2, 6], [4, 8]]] >>> permutedims(b, (1, 2, 0)) [[[1, 5], [2, 6]], [[3, 7], [4, 8]]] ``Permutation`` objects are also allowed: >>> from sympy.combinatorics import Permutation >>> permutedims(b, Permutation([1, 2, 0])) [[[1, 5], [2, 6]], [[3, 7], [4, 8]]] """ if not isinstance(expr, NDimArray): raise TypeError("expression has to be an N-dim array") from sympy.combinatorics import Permutation if not isinstance(perm, Permutation): perm = Permutation(list(perm)) if perm.size != expr.rank(): raise ValueError("wrong permutation size") # Get the inverse permutation: iperm = ~perm indices_span = perm([range(i) for i in expr.shape]) new_array = [None]*len(expr) for i, idx in enumerate(itertools.product(*indices_span)): t = iperm(idx) new_array[i] = expr[t] new_shape = perm(expr.shape) return type(expr)(new_array, new_shape)