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