Source code for sympy.physics.vector.dyadic

from sympy.core.backend import sympify, Add, ImmutableMatrix as Matrix
from sympy.core.compatibility import unicode
from .printing import (VectorLatexPrinter, VectorPrettyPrinter,
                       VectorStrPrinter)

__all__ = ['Dyadic']


[docs]class Dyadic(object): """A Dyadic object. See: http://en.wikipedia.org/wiki/Dyadic_tensor Kane, T., Levinson, D. Dynamics Theory and Applications. 1985 McGraw-Hill A more powerful way to represent a rigid body's inertia. While it is more complex, by choosing Dyadic components to be in body fixed basis vectors, the resulting matrix is equivalent to the inertia tensor. """ def __init__(self, inlist): """ Just like Vector's init, you shouldn't call this unless creating a zero dyadic. zd = Dyadic(0) Stores a Dyadic as a list of lists; the inner list has the measure number and the two unit vectors; the outerlist holds each unique unit vector pair. """ self.args = [] if inlist == 0: inlist = [] while len(inlist) != 0: added = 0 for i, v in enumerate(self.args): if ((str(inlist[0][1]) == str(self.args[i][1])) and (str(inlist[0][2]) == str(self.args[i][2]))): self.args[i] = (self.args[i][0] + inlist[0][0], inlist[0][1], inlist[0][2]) inlist.remove(inlist[0]) added = 1 break if added != 1: self.args.append(inlist[0]) inlist.remove(inlist[0]) i = 0 # This code is to remove empty parts from the list while i < len(self.args): if ((self.args[i][0] == 0) | (self.args[i][1] == 0) | (self.args[i][2] == 0)): self.args.remove(self.args[i]) i -= 1 i += 1 def __add__(self, other): """The add operator for Dyadic. """ other = _check_dyadic(other) return Dyadic(self.args + other.args) def __and__(self, other): """The inner product operator for a Dyadic and a Dyadic or Vector. Parameters ========== other : Dyadic or Vector The other Dyadic or Vector to take the inner product with Examples ======== >>> from sympy.physics.vector import ReferenceFrame, outer >>> N = ReferenceFrame('N') >>> D1 = outer(N.x, N.y) >>> D2 = outer(N.y, N.y) >>> D1.dot(D2) (N.x|N.y) >>> D1.dot(N.y) N.x """ from sympy.physics.vector.vector import Vector, _check_vector if isinstance(other, Dyadic): other = _check_dyadic(other) ol = Dyadic(0) for i, v in enumerate(self.args): for i2, v2 in enumerate(other.args): ol += v[0] * v2[0] * (v[2] & v2[1]) * (v[1] | v2[2]) else: other = _check_vector(other) ol = Vector(0) for i, v in enumerate(self.args): ol += v[0] * v[1] * (v[2] & other) return ol def __div__(self, other): """Divides the Dyadic by a sympifyable expression. """ return self.__mul__(1 / other) __truediv__ = __div__ def __eq__(self, other): """Tests for equality. Is currently weak; needs stronger comparison testing """ if other == 0: other = Dyadic(0) other = _check_dyadic(other) if (self.args == []) and (other.args == []): return True elif (self.args == []) or (other.args == []): return False return set(self.args) == set(other.args) def __mul__(self, other): """Multiplies the Dyadic by a sympifyable expression. Parameters ========== other : Sympafiable The scalar to multiply this Dyadic with Examples ======== >>> from sympy.physics.vector import ReferenceFrame, outer >>> N = ReferenceFrame('N') >>> d = outer(N.x, N.x) >>> 5 * d 5*(N.x|N.x) """ newlist = [v for v in self.args] for i, v in enumerate(newlist): newlist[i] = (sympify(other) * newlist[i][0], newlist[i][1], newlist[i][2]) return Dyadic(newlist) def __ne__(self, other): return not self.__eq__(other) def __neg__(self): return self * -1 def _latex(self, printer=None): ar = self.args # just to shorten things if len(ar) == 0: return str(0) ol = [] # output list, to be concatenated to a string mlp = VectorLatexPrinter() for i, v in enumerate(ar): # if the coef of the dyadic is 1, we skip the 1 if ar[i][0] == 1: ol.append(' + ' + mlp.doprint(ar[i][1]) + r"\otimes " + mlp.doprint(ar[i][2])) # if the coef of the dyadic is -1, we skip the 1 elif ar[i][0] == -1: ol.append(' - ' + mlp.doprint(ar[i][1]) + r"\otimes " + mlp.doprint(ar[i][2])) # If the coefficient of the dyadic is not 1 or -1, # we might wrap it in parentheses, for readability. elif ar[i][0] != 0: arg_str = mlp.doprint(ar[i][0]) if isinstance(ar[i][0], Add): arg_str = '(%s)' % arg_str if arg_str.startswith('-'): arg_str = arg_str[1:] str_start = ' - ' else: str_start = ' + ' ol.append(str_start + arg_str + mlp.doprint(ar[i][1]) + r"\otimes " + mlp.doprint(ar[i][2])) outstr = ''.join(ol) if outstr.startswith(' + '): outstr = outstr[3:] elif outstr.startswith(' '): outstr = outstr[1:] return outstr def _pretty(self, printer=None): e = self class Fake(object): baseline = 0 def render(self, *args, **kwargs): ar = e.args # just to shorten things settings = printer._settings if printer else {} if printer: use_unicode = printer._use_unicode else: from sympy.printing.pretty.pretty_symbology import ( pretty_use_unicode) use_unicode = pretty_use_unicode() mpp = printer if printer else VectorPrettyPrinter(settings) if len(ar) == 0: return unicode(0) bar = u"\N{CIRCLED TIMES}" if use_unicode else "|" ol = [] # output list, to be concatenated to a string for i, v in enumerate(ar): # if the coef of the dyadic is 1, we skip the 1 if ar[i][0] == 1: ol.extend([u" + ", mpp.doprint(ar[i][1]), bar, mpp.doprint(ar[i][2])]) # if the coef of the dyadic is -1, we skip the 1 elif ar[i][0] == -1: ol.extend([u" - ", mpp.doprint(ar[i][1]), bar, mpp.doprint(ar[i][2])]) # If the coefficient of the dyadic is not 1 or -1, # we might wrap it in parentheses, for readability. elif ar[i][0] != 0: if isinstance(ar[i][0], Add): arg_str = mpp._print( ar[i][0]).parens()[0] else: arg_str = mpp.doprint(ar[i][0]) if arg_str.startswith(u"-"): arg_str = arg_str[1:] str_start = u" - " else: str_start = u" + " ol.extend([str_start, arg_str, u" ", mpp.doprint(ar[i][1]), bar, mpp.doprint(ar[i][2])]) outstr = u"".join(ol) if outstr.startswith(u" + "): outstr = outstr[3:] elif outstr.startswith(" "): outstr = outstr[1:] return outstr return Fake() def __rand__(self, other): """The inner product operator for a Vector or Dyadic, and a Dyadic This is for: Vector dot Dyadic Parameters ========== other : Vector The vector we are dotting with Examples ======== >>> from sympy.physics.vector import ReferenceFrame, dot, outer >>> N = ReferenceFrame('N') >>> d = outer(N.x, N.x) >>> dot(N.x, d) N.x """ from sympy.physics.vector.vector import Vector, _check_vector other = _check_vector(other) ol = Vector(0) for i, v in enumerate(self.args): ol += v[0] * v[2] * (v[1] & other) return ol def __rsub__(self, other): return (-1 * self) + other def __rxor__(self, other): """For a cross product in the form: Vector x Dyadic Parameters ========== other : Vector The Vector that we are crossing this Dyadic with Examples ======== >>> from sympy.physics.vector import ReferenceFrame, outer, cross >>> N = ReferenceFrame('N') >>> d = outer(N.x, N.x) >>> cross(N.y, d) - (N.z|N.x) """ from sympy.physics.vector.vector import _check_vector other = _check_vector(other) ol = Dyadic(0) for i, v in enumerate(self.args): ol += v[0] * ((other ^ v[1]) | v[2]) return ol def __str__(self, printer=None): """Printing method. """ ar = self.args # just to shorten things if len(ar) == 0: return str(0) ol = [] # output list, to be concatenated to a string for i, v in enumerate(ar): # if the coef of the dyadic is 1, we skip the 1 if ar[i][0] == 1: ol.append(' + (' + str(ar[i][1]) + '|' + str(ar[i][2]) + ')') # if the coef of the dyadic is -1, we skip the 1 elif ar[i][0] == -1: ol.append(' - (' + str(ar[i][1]) + '|' + str(ar[i][2]) + ')') # If the coefficient of the dyadic is not 1 or -1, # we might wrap it in parentheses, for readability. elif ar[i][0] != 0: arg_str = VectorStrPrinter().doprint(ar[i][0]) if isinstance(ar[i][0], Add): arg_str = "(%s)" % arg_str if arg_str[0] == '-': arg_str = arg_str[1:] str_start = ' - ' else: str_start = ' + ' ol.append(str_start + arg_str + '*(' + str(ar[i][1]) + '|' + str(ar[i][2]) + ')') outstr = ''.join(ol) if outstr.startswith(' + '): outstr = outstr[3:] elif outstr.startswith(' '): outstr = outstr[1:] return outstr def __sub__(self, other): """The subtraction operator. """ return self.__add__(other * -1) def __xor__(self, other): """For a cross product in the form: Dyadic x Vector. Parameters ========== other : Vector The Vector that we are crossing this Dyadic with Examples ======== >>> from sympy.physics.vector import ReferenceFrame, outer, cross >>> N = ReferenceFrame('N') >>> d = outer(N.x, N.x) >>> cross(d, N.y) (N.x|N.z) """ from sympy.physics.vector.vector import _check_vector other = _check_vector(other) ol = Dyadic(0) for i, v in enumerate(self.args): ol += v[0] * (v[1] | (v[2] ^ other)) return ol _sympystr = __str__ _sympyrepr = _sympystr __repr__ = __str__ __radd__ = __add__ __rmul__ = __mul__
[docs] def express(self, frame1, frame2=None): """Expresses this Dyadic in alternate frame(s) The first frame is the list side expression, the second frame is the right side; if Dyadic is in form A.x|B.y, you can express it in two different frames. If no second frame is given, the Dyadic is expressed in only one frame. Calls the global express function Parameters ========== frame1 : ReferenceFrame The frame to express the left side of the Dyadic in frame2 : ReferenceFrame If provided, the frame to express the right side of the Dyadic in Examples ======== >>> from sympy.physics.vector import ReferenceFrame, outer, dynamicsymbols >>> N = ReferenceFrame('N') >>> q = dynamicsymbols('q') >>> B = N.orientnew('B', 'Axis', [q, N.z]) >>> d = outer(N.x, N.x) >>> d.express(B, N) cos(q)*(B.x|N.x) - sin(q)*(B.y|N.x) """ from sympy.physics.vector.functions import express return express(self, frame1, frame2)
[docs] def to_matrix(self, reference_frame, second_reference_frame=None): """Returns the matrix form of the dyadic with respect to one or two reference frames. Parameters ---------- reference_frame : ReferenceFrame The reference frame that the rows and columns of the matrix correspond to. If a second reference frame is provided, this only corresponds to the rows of the matrix. second_reference_frame : ReferenceFrame, optional, default=None The reference frame that the columns of the matrix correspond to. Returns ------- matrix : ImmutableMatrix, shape(3,3) The matrix that gives the 2D tensor form. Examples ======== >>> from sympy import symbols >>> from sympy.physics.vector import ReferenceFrame, Vector >>> Vector.simp = True >>> from sympy.physics.mechanics import inertia >>> Ixx, Iyy, Izz, Ixy, Iyz, Ixz = symbols('Ixx, Iyy, Izz, Ixy, Iyz, Ixz') >>> N = ReferenceFrame('N') >>> inertia_dyadic = inertia(N, Ixx, Iyy, Izz, Ixy, Iyz, Ixz) >>> inertia_dyadic.to_matrix(N) Matrix([ [Ixx, Ixy, Ixz], [Ixy, Iyy, Iyz], [Ixz, Iyz, Izz]]) >>> beta = symbols('beta') >>> A = N.orientnew('A', 'Axis', (beta, N.x)) >>> inertia_dyadic.to_matrix(A) Matrix([ [ Ixx, Ixy*cos(beta) + Ixz*sin(beta), -Ixy*sin(beta) + Ixz*cos(beta)], [ Ixy*cos(beta) + Ixz*sin(beta), Iyy*cos(2*beta)/2 + Iyy/2 + Iyz*sin(2*beta) - Izz*cos(2*beta)/2 + Izz/2, -Iyy*sin(2*beta)/2 + Iyz*cos(2*beta) + Izz*sin(2*beta)/2], [-Ixy*sin(beta) + Ixz*cos(beta), -Iyy*sin(2*beta)/2 + Iyz*cos(2*beta) + Izz*sin(2*beta)/2, -Iyy*cos(2*beta)/2 + Iyy/2 - Iyz*sin(2*beta) + Izz*cos(2*beta)/2 + Izz/2]]) """ if second_reference_frame is None: second_reference_frame = reference_frame return Matrix([i.dot(self).dot(j) for i in reference_frame for j in second_reference_frame]).reshape(3, 3)
[docs] def doit(self, **hints): """Calls .doit() on each term in the Dyadic""" return sum([Dyadic([(v[0].doit(**hints), v[1], v[2])]) for v in self.args], Dyadic(0))
[docs] def dt(self, frame): """Take the time derivative of this Dyadic in a frame. This function calls the global time_derivative method Parameters ========== frame : ReferenceFrame The frame to take the time derivative in Examples ======== >>> from sympy.physics.vector import ReferenceFrame, outer, dynamicsymbols >>> N = ReferenceFrame('N') >>> q = dynamicsymbols('q') >>> B = N.orientnew('B', 'Axis', [q, N.z]) >>> d = outer(N.x, N.x) >>> d.dt(B) - q'*(N.y|N.x) - q'*(N.x|N.y) """ from sympy.physics.vector.functions import time_derivative return time_derivative(self, frame)
[docs] def simplify(self): """Returns a simplified Dyadic.""" out = Dyadic(0) for v in self.args: out += Dyadic([(v[0].simplify(), v[1], v[2])]) return out
[docs] def subs(self, *args, **kwargs): """Substituion on the Dyadic. Examples ======== >>> from sympy.physics.vector import ReferenceFrame >>> from sympy import Symbol >>> N = ReferenceFrame('N') >>> s = Symbol('s') >>> a = s * (N.x|N.x) >>> a.subs({s: 2}) 2*(N.x|N.x) """ return sum([Dyadic([(v[0].subs(*args, **kwargs), v[1], v[2])]) for v in self.args], Dyadic(0))
[docs] def applyfunc(self, f): """Apply a function to each component of a Dyadic.""" if not callable(f): raise TypeError("`f` must be callable.") out = Dyadic(0) for a, b, c in self.args: out += f(a) * (b|c) return out
dot = __and__ cross = __xor__
def _check_dyadic(other): if not isinstance(other, Dyadic): raise TypeError('A Dyadic must be supplied') return other