from sympy.vector.coordsysrect import CoordSys3D
from sympy.vector.scalar import BaseScalar
from sympy.vector.vector import Vector, BaseVector
from sympy.vector.operators import gradient, curl, divergence
from sympy import diff, integrate, S, simplify
from sympy.core import sympify
from sympy.vector.dyadic import Dyadic
[docs]def express(expr, system, system2=None, variables=False):
"""
Global function for 'express' functionality.
Re-expresses a Vector, Dyadic or scalar(sympyfiable) in the given
coordinate system.
If 'variables' is True, then the coordinate variables (base scalars)
of other coordinate systems present in the vector/scalar field or
dyadic are also substituted in terms of the base scalars of the
given system.
Parameters
==========
expr : Vector/Dyadic/scalar(sympyfiable)
The expression to re-express in CoordSys3D 'system'
system: CoordSys3D
The coordinate system the expr is to be expressed in
system2: CoordSys3D
The other coordinate system required for re-expression
(only for a Dyadic Expr)
variables : boolean
Specifies whether to substitute the coordinate variables present
in expr, in terms of those of parameter system
Examples
========
>>> from sympy.vector import CoordSys3D
>>> from sympy import Symbol, cos, sin
>>> N = CoordSys3D('N')
>>> q = Symbol('q')
>>> B = N.orient_new_axis('B', q, N.k)
>>> from sympy.vector import express
>>> express(B.i, N)
(cos(q))*N.i + (sin(q))*N.j
>>> express(N.x, B, variables=True)
-sin(q)*B.y + cos(q)*B.x
>>> d = N.i.outer(N.i)
>>> express(d, B, N) == (cos(q))*(B.i|N.i) + (-sin(q))*(B.j|N.i)
True
"""
if expr == 0 or expr == Vector.zero:
return expr
if not isinstance(system, CoordSys3D):
raise TypeError("system should be a CoordSys3D \
instance")
if isinstance(expr, Vector):
if system2 is not None:
raise ValueError("system2 should not be provided for \
Vectors")
# Given expr is a Vector
if variables:
# If variables attribute is True, substitute
# the coordinate variables in the Vector
system_list = []
for x in expr.atoms(BaseScalar, BaseVector):
if x.system != system:
system_list.append(x.system)
system_list = set(system_list)
subs_dict = {}
for f in system_list:
subs_dict.update(f.scalar_map(system))
expr = expr.subs(subs_dict)
# Re-express in this coordinate system
outvec = Vector.zero
parts = expr.separate()
for x in parts:
if x != system:
temp = system.rotation_matrix(x) * parts[x].to_matrix(x)
outvec += matrix_to_vector(temp, system)
else:
outvec += parts[x]
return outvec
elif isinstance(expr, Dyadic):
if system2 is None:
system2 = system
if not isinstance(system2, CoordSys3D):
raise TypeError("system2 should be a CoordSys3D \
instance")
outdyad = Dyadic.zero
var = variables
for k, v in expr.components.items():
outdyad += (express(v, system, variables=var) *
(express(k.args[0], system, variables=var) |
express(k.args[1], system2, variables=var)))
return outdyad
else:
if system2 is not None:
raise ValueError("system2 should not be provided for \
Vectors")
if variables:
# Given expr is a scalar field
system_set = set([])
expr = sympify(expr)
# Subsitute all the coordinate variables
for x in expr.atoms(BaseScalar):
if x.system != system:
system_set.add(x.system)
subs_dict = {}
for f in system_set:
subs_dict.update(f.scalar_map(system))
return expr.subs(subs_dict)
return expr
def directional_derivative(scalar, vect):
"""
Returns the directional derivative of a scalar field computed along a given vector
in given coordinate system.
Parameters
==========
scalar : SymPy Expr
The scalar field to compute the gradient of
vect : Vector
The vector operand
coord_sys : CoordSys3D
The coordinate system to calculate the gradient in
Examples
========
>>> from sympy.vector import CoordSys3D, directional_derivative
>>> R = CoordSys3D('R')
>>> f1 = R.x*R.y*R.z
>>> v1 = 3*R.i + 4*R.j + R.k
>>> directional_derivative(f1, v1)
R.x*R.y + 4*R.x*R.z + 3*R.y*R.z
>>> f2 = 5*R.x**2*R.z
>>> directional_derivative(f2, v1)
5*R.x**2 + 30*R.x*R.z
"""
return gradient(scalar).dot(vect).doit()
[docs]def is_conservative(field):
"""
Checks if a field is conservative.
Paramaters
==========
field : Vector
The field to check for conservative property
Examples
========
>>> from sympy.vector import CoordSys3D
>>> from sympy.vector import is_conservative
>>> R = CoordSys3D('R')
>>> is_conservative(R.y*R.z*R.i + R.x*R.z*R.j + R.x*R.y*R.k)
True
>>> is_conservative(R.z*R.j)
False
"""
# Field is conservative irrespective of system
# Take the first coordinate system in the result of the
# separate method of Vector
if not isinstance(field, Vector):
raise TypeError("field should be a Vector")
if field == Vector.zero:
return True
return curl(field).simplify() == Vector.zero
[docs]def is_solenoidal(field):
"""
Checks if a field is solenoidal.
Paramaters
==========
field : Vector
The field to check for solenoidal property
Examples
========
>>> from sympy.vector import CoordSys3D
>>> from sympy.vector import is_solenoidal
>>> R = CoordSys3D('R')
>>> is_solenoidal(R.y*R.z*R.i + R.x*R.z*R.j + R.x*R.y*R.k)
True
>>> is_solenoidal(R.y * R.j)
False
"""
# Field is solenoidal irrespective of system
# Take the first coordinate system in the result of the
# separate method in Vector
if not isinstance(field, Vector):
raise TypeError("field should be a Vector")
if field == Vector.zero:
return True
return divergence(field).simplify() == S(0)
[docs]def scalar_potential(field, coord_sys):
"""
Returns the scalar potential function of a field in a given
coordinate system (without the added integration constant).
Parameters
==========
field : Vector
The vector field whose scalar potential function is to be
calculated
coord_sys : CoordSys3D
The coordinate system to do the calculation in
Examples
========
>>> from sympy.vector import CoordSys3D
>>> from sympy.vector import scalar_potential, gradient
>>> R = CoordSys3D('R')
>>> scalar_potential(R.k, R) == R.z
True
>>> scalar_field = 2*R.x**2*R.y*R.z
>>> grad_field = gradient(scalar_field)
>>> scalar_potential(grad_field, R)
2*R.x**2*R.y*R.z
"""
# Check whether field is conservative
if not is_conservative(field):
raise ValueError("Field is not conservative")
if field == Vector.zero:
return S(0)
# Express the field exntirely in coord_sys
# Subsitute coordinate variables also
if not isinstance(coord_sys, CoordSys3D):
raise TypeError("coord_sys must be a CoordSys3D")
field = express(field, coord_sys, variables=True)
dimensions = coord_sys.base_vectors()
scalars = coord_sys.base_scalars()
# Calculate scalar potential function
temp_function = integrate(field.dot(dimensions[0]), scalars[0])
for i, dim in enumerate(dimensions[1:]):
partial_diff = diff(temp_function, scalars[i + 1])
partial_diff = field.dot(dim) - partial_diff
temp_function += integrate(partial_diff, scalars[i + 1])
return temp_function
[docs]def scalar_potential_difference(field, coord_sys, point1, point2):
"""
Returns the scalar potential difference between two points in a
certain coordinate system, wrt a given field.
If a scalar field is provided, its values at the two points are
considered. If a conservative vector field is provided, the values
of its scalar potential function at the two points are used.
Returns (potential at point2) - (potential at point1)
The position vectors of the two Points are calculated wrt the
origin of the coordinate system provided.
Parameters
==========
field : Vector/Expr
The field to calculate wrt
coord_sys : CoordSys3D
The coordinate system to do the calculations in
point1 : Point
The initial Point in given coordinate system
position2 : Point
The second Point in the given coordinate system
Examples
========
>>> from sympy.vector import CoordSys3D, Point
>>> from sympy.vector import scalar_potential_difference
>>> R = CoordSys3D('R')
>>> P = R.origin.locate_new('P', R.x*R.i + R.y*R.j + R.z*R.k)
>>> vectfield = 4*R.x*R.y*R.i + 2*R.x**2*R.j
>>> scalar_potential_difference(vectfield, R, R.origin, P)
2*R.x**2*R.y
>>> Q = R.origin.locate_new('O', 3*R.i + R.j + 2*R.k)
>>> scalar_potential_difference(vectfield, R, P, Q)
-2*R.x**2*R.y + 18
"""
if not isinstance(coord_sys, CoordSys3D):
raise TypeError("coord_sys must be a CoordSys3D")
if isinstance(field, Vector):
# Get the scalar potential function
scalar_fn = scalar_potential(field, coord_sys)
else:
# Field is a scalar
scalar_fn = field
# Express positions in required coordinate system
origin = coord_sys.origin
position1 = express(point1.position_wrt(origin), coord_sys,
variables=True)
position2 = express(point2.position_wrt(origin), coord_sys,
variables=True)
# Get the two positions as substitution dicts for coordinate variables
subs_dict1 = {}
subs_dict2 = {}
scalars = coord_sys.base_scalars()
for i, x in enumerate(coord_sys.base_vectors()):
subs_dict1[scalars[i]] = x.dot(position1)
subs_dict2[scalars[i]] = x.dot(position2)
return scalar_fn.subs(subs_dict2) - scalar_fn.subs(subs_dict1)
[docs]def matrix_to_vector(matrix, system):
"""
Converts a vector in matrix form to a Vector instance.
It is assumed that the elements of the Matrix represent the
measure numbers of the components of the vector along basis
vectors of 'system'.
Parameters
==========
matrix : SymPy Matrix, Dimensions: (3, 1)
The matrix to be converted to a vector
system : CoordSys3D
The coordinate system the vector is to be defined in
Examples
========
>>> from sympy import ImmutableMatrix as Matrix
>>> m = Matrix([1, 2, 3])
>>> from sympy.vector import CoordSys3D, matrix_to_vector
>>> C = CoordSys3D('C')
>>> v = matrix_to_vector(m, C)
>>> v
C.i + 2*C.j + 3*C.k
>>> v.to_matrix(C) == m
True
"""
outvec = Vector.zero
vects = system.base_vectors()
for i, x in enumerate(matrix):
outvec += x * vects[i]
return outvec
def _path(from_object, to_object):
"""
Calculates the 'path' of objects starting from 'from_object'
to 'to_object', along with the index of the first common
ancestor in the tree.
Returns (index, list) tuple.
"""
if from_object._root != to_object._root:
raise ValueError("No connecting path found between " +
str(from_object) + " and " + str(to_object))
other_path = []
obj = to_object
while obj._parent is not None:
other_path.append(obj)
obj = obj._parent
other_path.append(obj)
object_set = set(other_path)
from_path = []
obj = from_object
while obj not in object_set:
from_path.append(obj)
obj = obj._parent
index = len(from_path)
i = other_path.index(obj)
while i >= 0:
from_path.append(other_path[i])
i -= 1
return index, from_path
def orthogonalize(*vlist, **kwargs):
"""
Takes a sequence of independent vectors and orthogonalizes them
using the Gram - Schmidt process. Returns a list of
orthogonal or orthonormal vectors.
Parameters
==========
vlist : sequence of independent vectors to be made orthogonal.
orthonormal : Optional parameter
Set to True if the the vectors returned should be
orthonormal.
Default: False
Examples
========
>>> from sympy.vector.coordsysrect import CoordSys3D
>>> from sympy.vector.vector import Vector, BaseVector
>>> from sympy.vector.functions import orthogonalize
>>> C = CoordSys3D('C')
>>> i, j, k = C.base_vectors()
>>> v1 = i + 2*j
>>> v2 = 2*i + 3*j
>>> orthogonalize(v1, v2)
[C.i + 2*C.j, 2/5*C.i + (-1/5)*C.j]
References
==========
.. [1] https://en.wikipedia.org/wiki/Gram-Schmidt_process
"""
orthonormal = kwargs.get('orthonormal', False)
if not all(isinstance(vec, Vector) for vec in vlist):
raise TypeError('Each element must be of Type Vector')
ortho_vlist = []
for i, term in enumerate(vlist):
for j in range(i):
term -= ortho_vlist[j].projection(vlist[i])
# TODO : The following line introduces a performance issue
# and needs to be changed once a good solution for issue #10279 is
# found.
if simplify(term).equals(Vector.zero):
raise ValueError("Vector set not linearly independent")
ortho_vlist.append(term)
if orthonormal:
ortho_vlist = [vec.normalize() for vec in ortho_vlist]
return ortho_vlist
