|
|
from sympy.core.backend import (diff, expand, sin, cos, sympify, eye, symbols, ImmutableMatrix as Matrix, MatrixBase)from sympy.core.symbol import (Dummy, Symbol)from sympy.simplify.trigsimp import trigsimpfrom sympy.solvers.solvers import solvefrom sympy.physics.vector.vector import Vector, _check_vectorfrom sympy.utilities.misc import translate
from warnings import warn
__all__ = ['CoordinateSym', 'ReferenceFrame']
class CoordinateSym(Symbol): """
A coordinate symbol/base scalar associated wrt a Reference Frame.
Ideally, users should not instantiate this class. Instances of this class must only be accessed through the corresponding frame as 'frame[index]'.
CoordinateSyms having the same frame and index parameters are equal (even though they may be instantiated separately).
Parameters ==========
name : string The display name of the CoordinateSym
frame : ReferenceFrame The reference frame this base scalar belongs to
index : 0, 1 or 2 The index of the dimension denoted by this coordinate variable
Examples ========
>>> from sympy.physics.vector import ReferenceFrame, CoordinateSym >>> A = ReferenceFrame('A') >>> A[1] A_y >>> type(A[0]) <class 'sympy.physics.vector.frame.CoordinateSym'> >>> a_y = CoordinateSym('a_y', A, 1) >>> a_y == A[1] True
"""
def __new__(cls, name, frame, index): # We can't use the cached Symbol.__new__ because this class depends on # frame and index, which are not passed to Symbol.__xnew__. assumptions = {} super()._sanitize(assumptions, cls) obj = super().__xnew__(cls, name, **assumptions) _check_frame(frame) if index not in range(0, 3): raise ValueError("Invalid index specified") obj._id = (frame, index) return obj
@property def frame(self): return self._id[0]
def __eq__(self, other): #Check if the other object is a CoordinateSym of the same frame #and same index if isinstance(other, CoordinateSym): if other._id == self._id: return True return False
def __ne__(self, other): return not self == other
def __hash__(self): return tuple((self._id[0].__hash__(), self._id[1])).__hash__()
class ReferenceFrame: """A reference frame in classical mechanics.
ReferenceFrame is a class used to represent a reference frame in classical mechanics. It has a standard basis of three unit vectors in the frame's x, y, and z directions.
It also can have a rotation relative to a parent frame; this rotation is defined by a direction cosine matrix relating this frame's basis vectors to the parent frame's basis vectors. It can also have an angular velocity vector, defined in another frame.
"""
_count = 0
def __init__(self, name, indices=None, latexs=None, variables=None): """ReferenceFrame initialization method.
A ReferenceFrame has a set of orthonormal basis vectors, along with orientations relative to other ReferenceFrames and angular velocities relative to other ReferenceFrames.
Parameters ==========
indices : tuple of str Enables the reference frame's basis unit vectors to be accessed by Python's square bracket indexing notation using the provided three indice strings and alters the printing of the unit vectors to reflect this choice. latexs : tuple of str Alters the LaTeX printing of the reference frame's basis unit vectors to the provided three valid LaTeX strings.
Examples ========
>>> from sympy.physics.vector import ReferenceFrame, vlatex >>> N = ReferenceFrame('N') >>> N.x N.x >>> O = ReferenceFrame('O', indices=('1', '2', '3')) >>> O.x O['1'] >>> O['1'] O['1'] >>> P = ReferenceFrame('P', latexs=('A1', 'A2', 'A3')) >>> vlatex(P.x) 'A1'
symbols() can be used to create multiple Reference Frames in one step, for example:
>>> from sympy.physics.vector import ReferenceFrame >>> from sympy import symbols >>> A, B, C = symbols('A B C', cls=ReferenceFrame) >>> D, E = symbols('D E', cls=ReferenceFrame, indices=('1', '2', '3')) >>> A[0] A_x >>> D.x D['1'] >>> E.y E['2'] >>> type(A) == type(D) True
"""
if not isinstance(name, str): raise TypeError('Need to supply a valid name') # The if statements below are for custom printing of basis-vectors for # each frame. # First case, when custom indices are supplied if indices is not None: if not isinstance(indices, (tuple, list)): raise TypeError('Supply the indices as a list') if len(indices) != 3: raise ValueError('Supply 3 indices') for i in indices: if not isinstance(i, str): raise TypeError('Indices must be strings') self.str_vecs = [(name + '[\'' + indices[0] + '\']'), (name + '[\'' + indices[1] + '\']'), (name + '[\'' + indices[2] + '\']')] self.pretty_vecs = [(name.lower() + "_" + indices[0]), (name.lower() + "_" + indices[1]), (name.lower() + "_" + indices[2])] self.latex_vecs = [(r"\mathbf{\hat{%s}_{%s}}" % (name.lower(), indices[0])), (r"\mathbf{\hat{%s}_{%s}}" % (name.lower(), indices[1])), (r"\mathbf{\hat{%s}_{%s}}" % (name.lower(), indices[2]))] self.indices = indices # Second case, when no custom indices are supplied else: self.str_vecs = [(name + '.x'), (name + '.y'), (name + '.z')] self.pretty_vecs = [name.lower() + "_x", name.lower() + "_y", name.lower() + "_z"] self.latex_vecs = [(r"\mathbf{\hat{%s}_x}" % name.lower()), (r"\mathbf{\hat{%s}_y}" % name.lower()), (r"\mathbf{\hat{%s}_z}" % name.lower())] self.indices = ['x', 'y', 'z'] # Different step, for custom latex basis vectors if latexs is not None: if not isinstance(latexs, (tuple, list)): raise TypeError('Supply the indices as a list') if len(latexs) != 3: raise ValueError('Supply 3 indices') for i in latexs: if not isinstance(i, str): raise TypeError('Latex entries must be strings') self.latex_vecs = latexs self.name = name self._var_dict = {} #The _dcm_dict dictionary will only store the dcms of adjacent parent-child #relationships. The _dcm_cache dictionary will store calculated dcm along with #all content of _dcm_dict for faster retrieval of dcms. self._dcm_dict = {} self._dcm_cache = {} self._ang_vel_dict = {} self._ang_acc_dict = {} self._dlist = [self._dcm_dict, self._ang_vel_dict, self._ang_acc_dict] self._cur = 0 self._x = Vector([(Matrix([1, 0, 0]), self)]) self._y = Vector([(Matrix([0, 1, 0]), self)]) self._z = Vector([(Matrix([0, 0, 1]), self)]) #Associate coordinate symbols wrt this frame if variables is not None: if not isinstance(variables, (tuple, list)): raise TypeError('Supply the variable names as a list/tuple') if len(variables) != 3: raise ValueError('Supply 3 variable names') for i in variables: if not isinstance(i, str): raise TypeError('Variable names must be strings') else: variables = [name + '_x', name + '_y', name + '_z'] self.varlist = (CoordinateSym(variables[0], self, 0), \ CoordinateSym(variables[1], self, 1), \ CoordinateSym(variables[2], self, 2)) ReferenceFrame._count += 1 self.index = ReferenceFrame._count
def __getitem__(self, ind): """
Returns basis vector for the provided index, if the index is a string.
If the index is a number, returns the coordinate variable correspon- -ding to that index. """
if not isinstance(ind, str): if ind < 3: return self.varlist[ind] else: raise ValueError("Invalid index provided") if self.indices[0] == ind: return self.x if self.indices[1] == ind: return self.y if self.indices[2] == ind: return self.z else: raise ValueError('Not a defined index')
def __iter__(self): return iter([self.x, self.y, self.z])
def __str__(self): """Returns the name of the frame. """ return self.name
__repr__ = __str__
def _dict_list(self, other, num): """Returns an inclusive list of reference frames that connect this
reference frame to the provided reference frame.
Parameters ========== other : ReferenceFrame The other reference frame to look for a connecting relationship to. num : integer ``0``, ``1``, and ``2`` will look for orientation, angular velocity, and angular acceleration relationships between the two frames, respectively.
Returns ======= list Inclusive list of reference frames that connect this reference frame to the other reference frame.
Examples ========
>>> from sympy.physics.vector import ReferenceFrame >>> A = ReferenceFrame('A') >>> B = ReferenceFrame('B') >>> C = ReferenceFrame('C') >>> D = ReferenceFrame('D') >>> B.orient_axis(A, A.x, 1.0) >>> C.orient_axis(B, B.x, 1.0) >>> D.orient_axis(C, C.x, 1.0) >>> D._dict_list(A, 0) [D, C, B, A]
Raises ======
ValueError When no path is found between the two reference frames or ``num`` is an incorrect value.
"""
connect_type = {0: 'orientation', 1: 'angular velocity', 2: 'angular acceleration'}
if num not in connect_type.keys(): raise ValueError('Valid values for num are 0, 1, or 2.')
possible_connecting_paths = [[self]] oldlist = [[]] while possible_connecting_paths != oldlist: oldlist = possible_connecting_paths[:] # make a copy for frame_list in possible_connecting_paths: frames_adjacent_to_last = frame_list[-1]._dlist[num].keys() for adjacent_frame in frames_adjacent_to_last: if adjacent_frame not in frame_list: connecting_path = frame_list + [adjacent_frame] if connecting_path not in possible_connecting_paths: possible_connecting_paths.append(connecting_path)
for connecting_path in oldlist: if connecting_path[-1] != other: possible_connecting_paths.remove(connecting_path) possible_connecting_paths.sort(key=len)
if len(possible_connecting_paths) != 0: return possible_connecting_paths[0] # selects the shortest path
msg = 'No connecting {} path found between {} and {}.' raise ValueError(msg.format(connect_type[num], self.name, other.name))
def _w_diff_dcm(self, otherframe): """Angular velocity from time differentiating the DCM. """ from sympy.physics.vector.functions import dynamicsymbols dcm2diff = otherframe.dcm(self) diffed = dcm2diff.diff(dynamicsymbols._t) angvelmat = diffed * dcm2diff.T w1 = trigsimp(expand(angvelmat[7]), recursive=True) w2 = trigsimp(expand(angvelmat[2]), recursive=True) w3 = trigsimp(expand(angvelmat[3]), recursive=True) return Vector([(Matrix([w1, w2, w3]), otherframe)])
def variable_map(self, otherframe): """
Returns a dictionary which expresses the coordinate variables of this frame in terms of the variables of otherframe.
If Vector.simp is True, returns a simplified version of the mapped values. Else, returns them without simplification.
Simplification of the expressions may take time.
Parameters ==========
otherframe : ReferenceFrame The other frame to map the variables to
Examples ========
>>> from sympy.physics.vector import ReferenceFrame, dynamicsymbols >>> A = ReferenceFrame('A') >>> q = dynamicsymbols('q') >>> B = A.orientnew('B', 'Axis', [q, A.z]) >>> A.variable_map(B) {A_x: B_x*cos(q(t)) - B_y*sin(q(t)), A_y: B_x*sin(q(t)) + B_y*cos(q(t)), A_z: B_z}
"""
_check_frame(otherframe) if (otherframe, Vector.simp) in self._var_dict: return self._var_dict[(otherframe, Vector.simp)] else: vars_matrix = self.dcm(otherframe) * Matrix(otherframe.varlist) mapping = {} for i, x in enumerate(self): if Vector.simp: mapping[self.varlist[i]] = trigsimp(vars_matrix[i], method='fu') else: mapping[self.varlist[i]] = vars_matrix[i] self._var_dict[(otherframe, Vector.simp)] = mapping return mapping
def ang_acc_in(self, otherframe): """Returns the angular acceleration Vector of the ReferenceFrame.
Effectively returns the Vector: ^N alpha ^B which represent the angular acceleration of B in N, where B is self, and N is otherframe.
Parameters ==========
otherframe : ReferenceFrame The ReferenceFrame which the angular acceleration is returned in.
Examples ========
>>> from sympy.physics.vector import ReferenceFrame >>> N = ReferenceFrame('N') >>> A = ReferenceFrame('A') >>> V = 10 * N.x >>> A.set_ang_acc(N, V) >>> A.ang_acc_in(N) 10*N.x
"""
_check_frame(otherframe) if otherframe in self._ang_acc_dict: return self._ang_acc_dict[otherframe] else: return self.ang_vel_in(otherframe).dt(otherframe)
def ang_vel_in(self, otherframe): """Returns the angular velocity Vector of the ReferenceFrame.
Effectively returns the Vector:
^N omega ^B
which represent the angular velocity of B in N, where B is self, and N is otherframe.
Parameters ==========
otherframe : ReferenceFrame The ReferenceFrame which the angular velocity is returned in.
Examples ========
>>> from sympy.physics.vector import ReferenceFrame >>> N = ReferenceFrame('N') >>> A = ReferenceFrame('A') >>> V = 10 * N.x >>> A.set_ang_vel(N, V) >>> A.ang_vel_in(N) 10*N.x
"""
_check_frame(otherframe) flist = self._dict_list(otherframe, 1) outvec = Vector(0) for i in range(len(flist) - 1): outvec += flist[i]._ang_vel_dict[flist[i + 1]] return outvec
def dcm(self, otherframe): r"""Returns the direction cosine matrix relative to the provided
reference frame.
The returned matrix can be used to express the orthogonal unit vectors of this frame in terms of the orthogonal unit vectors of ``otherframe``.
Parameters ==========
otherframe : ReferenceFrame The reference frame which the direction cosine matrix of this frame is formed relative to.
Examples ========
The following example rotates the reference frame A relative to N by a simple rotation and then calculates the direction cosine matrix of N relative to A.
>>> from sympy import symbols, sin, cos >>> from sympy.physics.vector import ReferenceFrame >>> q1 = symbols('q1') >>> N = ReferenceFrame('N') >>> A = N.orientnew('A', 'Axis', (q1, N.x)) >>> N.dcm(A) Matrix([ [1, 0, 0], [0, cos(q1), -sin(q1)], [0, sin(q1), cos(q1)]])
The second row of the above direction cosine matrix represents the ``N.y`` unit vector in N expressed in A. Like so:
>>> Ny = 0*A.x + cos(q1)*A.y - sin(q1)*A.z
Thus, expressing ``N.y`` in A should return the same result:
>>> N.y.express(A) cos(q1)*A.y - sin(q1)*A.z
Notes =====
It is import to know what form of the direction cosine matrix is returned. If ``B.dcm(A)`` is called, it means the "direction cosine matrix of B relative to A". This is the matrix :math:`^{\mathbf{A}} \mathbf{R} ^{\mathbf{B}}` shown in the following relationship:
.. math::
\begin{bmatrix} \hat{\mathbf{b}}_1 \\ \hat{\mathbf{b}}_2 \\ \hat{\mathbf{b}}_3 \end{bmatrix} = {}^A\mathbf{R}^B \begin{bmatrix} \hat{\mathbf{a}}_1 \\ \hat{\mathbf{a}}_2 \\ \hat{\mathbf{a}}_3 \end{bmatrix}.
:math:`{}^A\mathbf{R}^B` is the matrix that expresses the B unit vectors in terms of the A unit vectors.
"""
_check_frame(otherframe) # Check if the dcm wrt that frame has already been calculated if otherframe in self._dcm_cache: return self._dcm_cache[otherframe] flist = self._dict_list(otherframe, 0) outdcm = eye(3) for i in range(len(flist) - 1): outdcm = outdcm * flist[i]._dcm_dict[flist[i + 1]] # After calculation, store the dcm in dcm cache for faster future # retrieval self._dcm_cache[otherframe] = outdcm otherframe._dcm_cache[self] = outdcm.T return outdcm
def _dcm(self, parent, parent_orient): # If parent.oreint(self) is already defined,then # update the _dcm_dict of parent while over write # all content of self._dcm_dict and self._dcm_cache # with new dcm relation. # Else update _dcm_cache and _dcm_dict of both # self and parent. frames = self._dcm_cache.keys() dcm_dict_del = [] dcm_cache_del = [] if parent in frames: for frame in frames: if frame in self._dcm_dict: dcm_dict_del += [frame] dcm_cache_del += [frame] # Reset the _dcm_cache of this frame, and remove it from the # _dcm_caches of the frames it is linked to. Also remove it from the # _dcm_dict of its parent for frame in dcm_dict_del: del frame._dcm_dict[self] for frame in dcm_cache_del: del frame._dcm_cache[self] # Reset the _dcm_dict self._dcm_dict = self._dlist[0] = {} # Reset the _dcm_cache self._dcm_cache = {}
else: #Check for loops and raise warning accordingly. visited = [] queue = list(frames) cont = True #Flag to control queue loop. while queue and cont: node = queue.pop(0) if node not in visited: visited.append(node) neighbors = node._dcm_dict.keys() for neighbor in neighbors: if neighbor == parent: warn('Loops are defined among the orientation of frames.' + \ ' This is likely not desired and may cause errors in your calculations.') cont = False break queue.append(neighbor)
# Add the dcm relationship to _dcm_dict self._dcm_dict.update({parent: parent_orient.T}) parent._dcm_dict.update({self: parent_orient}) # Update the dcm cache self._dcm_cache.update({parent: parent_orient.T}) parent._dcm_cache.update({self: parent_orient})
def orient_axis(self, parent, axis, angle): """Sets the orientation of this reference frame with respect to a
parent reference frame by rotating through an angle about an axis fixed in the parent reference frame.
Parameters ==========
parent : ReferenceFrame Reference frame that this reference frame will be rotated relative to. axis : Vector Vector fixed in the parent frame about about which this frame is rotated. It need not be a unit vector and the rotation follows the right hand rule. angle : sympifiable Angle in radians by which it the frame is to be rotated.
Warns ======
UserWarning If the orientation creates a kinematic loop.
Examples ========
Setup variables for the examples:
>>> from sympy import symbols >>> from sympy.physics.vector import ReferenceFrame >>> q1 = symbols('q1') >>> N = ReferenceFrame('N') >>> B = ReferenceFrame('B') >>> B.orient_axis(N, N.x, q1)
The ``orient_axis()`` method generates a direction cosine matrix and its transpose which defines the orientation of B relative to N and vice versa. Once orient is called, ``dcm()`` outputs the appropriate direction cosine matrix:
>>> B.dcm(N) Matrix([ [1, 0, 0], [0, cos(q1), sin(q1)], [0, -sin(q1), cos(q1)]]) >>> N.dcm(B) Matrix([ [1, 0, 0], [0, cos(q1), -sin(q1)], [0, sin(q1), cos(q1)]])
The following two lines show that the sense of the rotation can be defined by negating the vector direction or the angle. Both lines produce the same result.
>>> B.orient_axis(N, -N.x, q1) >>> B.orient_axis(N, N.x, -q1)
"""
from sympy.physics.vector.functions import dynamicsymbols _check_frame(parent)
if not isinstance(axis, Vector) and isinstance(angle, Vector): axis, angle = angle, axis
axis = _check_vector(axis) amount = sympify(angle) theta = amount parent_orient_axis = []
if not axis.dt(parent) == 0: raise ValueError('Axis cannot be time-varying.') unit_axis = axis.express(parent).normalize() unit_col = unit_axis.args[0][0] parent_orient_axis = ( (eye(3) - unit_col * unit_col.T) * cos(theta) + Matrix([[0, -unit_col[2], unit_col[1]], [unit_col[2], 0, -unit_col[0]], [-unit_col[1], unit_col[0], 0]]) * sin(theta) + unit_col * unit_col.T)
self._dcm(parent, parent_orient_axis)
thetad = (amount).diff(dynamicsymbols._t) wvec = thetad*axis.express(parent).normalize() self._ang_vel_dict.update({parent: wvec}) parent._ang_vel_dict.update({self: -wvec}) self._var_dict = {}
def orient_explicit(self, parent, dcm): """Sets the orientation of this reference frame relative to a parent
reference frame by explicitly setting the direction cosine matrix.
Parameters ==========
parent : ReferenceFrame Reference frame that this reference frame will be rotated relative to. dcm : Matrix, shape(3, 3) Direction cosine matrix that specifies the relative rotation between the two reference frames.
Warns ======
UserWarning If the orientation creates a kinematic loop.
Examples ========
Setup variables for the examples:
>>> from sympy import symbols, Matrix, sin, cos >>> from sympy.physics.vector import ReferenceFrame >>> q1 = symbols('q1') >>> A = ReferenceFrame('A') >>> B = ReferenceFrame('B') >>> N = ReferenceFrame('N')
A simple rotation of ``A`` relative to ``N`` about ``N.x`` is defined by the following direction cosine matrix:
>>> dcm = Matrix([[1, 0, 0], ... [0, cos(q1), -sin(q1)], ... [0, sin(q1), cos(q1)]]) >>> A.orient_explicit(N, dcm) >>> A.dcm(N) Matrix([ [1, 0, 0], [0, cos(q1), sin(q1)], [0, -sin(q1), cos(q1)]])
This is equivalent to using ``orient_axis()``:
>>> B.orient_axis(N, N.x, q1) >>> B.dcm(N) Matrix([ [1, 0, 0], [0, cos(q1), sin(q1)], [0, -sin(q1), cos(q1)]])
**Note carefully that** ``N.dcm(B)`` **(the transpose) would be passed into** ``orient_explicit()`` **for** ``A.dcm(N)`` **to match** ``B.dcm(N)``:
>>> A.orient_explicit(N, N.dcm(B)) >>> A.dcm(N) Matrix([ [1, 0, 0], [0, cos(q1), sin(q1)], [0, -sin(q1), cos(q1)]])
"""
_check_frame(parent) # amounts must be a Matrix type object # (e.g. sympy.matrices.dense.MutableDenseMatrix). if not isinstance(dcm, MatrixBase): raise TypeError("Amounts must be a SymPy Matrix type object.")
parent_orient_dcm = [] parent_orient_dcm = dcm
self._dcm(parent, parent_orient_dcm)
wvec = self._w_diff_dcm(parent) self._ang_vel_dict.update({parent: wvec}) parent._ang_vel_dict.update({self: -wvec}) self._var_dict = {}
def _rot(self, axis, angle): """DCM for simple axis 1,2,or 3 rotations.""" if axis == 1: return Matrix([[1, 0, 0], [0, cos(angle), -sin(angle)], [0, sin(angle), cos(angle)]]) elif axis == 2: return Matrix([[cos(angle), 0, sin(angle)], [0, 1, 0], [-sin(angle), 0, cos(angle)]]) elif axis == 3: return Matrix([[cos(angle), -sin(angle), 0], [sin(angle), cos(angle), 0], [0, 0, 1]])
def orient_body_fixed(self, parent, angles, rotation_order): """Rotates this reference frame relative to the parent reference frame
by right hand rotating through three successive body fixed simple axis rotations. Each subsequent axis of rotation is about the "body fixed" unit vectors of a new intermediate reference frame. This type of rotation is also referred to rotating through the `Euler and Tait-Bryan Angles`_.
.. _Euler and Tait-Bryan Angles: https://en.wikipedia.org/wiki/Euler_angles
Parameters ==========
parent : ReferenceFrame Reference frame that this reference frame will be rotated relative to. angles : 3-tuple of sympifiable Three angles in radians used for the successive rotations. rotation_order : 3 character string or 3 digit integer Order of the rotations about each intermediate reference frames' unit vectors. The Euler rotation about the X, Z', X'' axes can be specified by the strings ``'XZX'``, ``'131'``, or the integer ``131``. There are 12 unique valid rotation orders (6 Euler and 6 Tait-Bryan): zxz, xyx, yzy, zyz, xzx, yxy, xyz, yzx, zxy, xzy, zyx, and yxz.
Warns ======
UserWarning If the orientation creates a kinematic loop.
Examples ========
Setup variables for the examples:
>>> from sympy import symbols >>> from sympy.physics.vector import ReferenceFrame >>> q1, q2, q3 = symbols('q1, q2, q3') >>> N = ReferenceFrame('N') >>> B = ReferenceFrame('B') >>> B1 = ReferenceFrame('B1') >>> B2 = ReferenceFrame('B2') >>> B3 = ReferenceFrame('B3')
For example, a classic Euler Angle rotation can be done by:
>>> B.orient_body_fixed(N, (q1, q2, q3), 'XYX') >>> B.dcm(N) Matrix([ [ cos(q2), sin(q1)*sin(q2), -sin(q2)*cos(q1)], [sin(q2)*sin(q3), -sin(q1)*sin(q3)*cos(q2) + cos(q1)*cos(q3), sin(q1)*cos(q3) + sin(q3)*cos(q1)*cos(q2)], [sin(q2)*cos(q3), -sin(q1)*cos(q2)*cos(q3) - sin(q3)*cos(q1), -sin(q1)*sin(q3) + cos(q1)*cos(q2)*cos(q3)]])
This rotates reference frame B relative to reference frame N through ``q1`` about ``N.x``, then rotates B again through ``q2`` about ``B.y``, and finally through ``q3`` about ``B.x``. It is equivalent to three successive ``orient_axis()`` calls:
>>> B1.orient_axis(N, N.x, q1) >>> B2.orient_axis(B1, B1.y, q2) >>> B3.orient_axis(B2, B2.x, q3) >>> B3.dcm(N) Matrix([ [ cos(q2), sin(q1)*sin(q2), -sin(q2)*cos(q1)], [sin(q2)*sin(q3), -sin(q1)*sin(q3)*cos(q2) + cos(q1)*cos(q3), sin(q1)*cos(q3) + sin(q3)*cos(q1)*cos(q2)], [sin(q2)*cos(q3), -sin(q1)*cos(q2)*cos(q3) - sin(q3)*cos(q1), -sin(q1)*sin(q3) + cos(q1)*cos(q2)*cos(q3)]])
Acceptable rotation orders are of length 3, expressed in as a string ``'XYZ'`` or ``'123'`` or integer ``123``. Rotations about an axis twice in a row are prohibited.
>>> B.orient_body_fixed(N, (q1, q2, 0), 'ZXZ') >>> B.orient_body_fixed(N, (q1, q2, 0), '121') >>> B.orient_body_fixed(N, (q1, q2, q3), 123)
"""
_check_frame(parent)
amounts = list(angles) for i, v in enumerate(amounts): if not isinstance(v, Vector): amounts[i] = sympify(v)
approved_orders = ('123', '231', '312', '132', '213', '321', '121', '131', '212', '232', '313', '323', '') # make sure XYZ => 123 rot_order = translate(str(rotation_order), 'XYZxyz', '123123') if rot_order not in approved_orders: raise TypeError('The rotation order is not a valid order.')
parent_orient_body = [] if not (len(amounts) == 3 & len(rot_order) == 3): raise TypeError('Body orientation takes 3 values & 3 orders') a1 = int(rot_order[0]) a2 = int(rot_order[1]) a3 = int(rot_order[2]) parent_orient_body = (self._rot(a1, amounts[0]) * self._rot(a2, amounts[1]) * self._rot(a3, amounts[2]))
self._dcm(parent, parent_orient_body)
try: from sympy.polys.polyerrors import CoercionFailed from sympy.physics.vector.functions import kinematic_equations q1, q2, q3 = amounts u1, u2, u3 = symbols('u1, u2, u3', cls=Dummy) templist = kinematic_equations([u1, u2, u3], [q1, q2, q3], 'body', rot_order) templist = [expand(i) for i in templist] td = solve(templist, [u1, u2, u3]) u1 = expand(td[u1]) u2 = expand(td[u2]) u3 = expand(td[u3]) wvec = u1 * self.x + u2 * self.y + u3 * self.z except (CoercionFailed, AssertionError): wvec = self._w_diff_dcm(parent) self._ang_vel_dict.update({parent: wvec}) parent._ang_vel_dict.update({self: -wvec}) self._var_dict = {}
def orient_space_fixed(self, parent, angles, rotation_order): """Rotates this reference frame relative to the parent reference frame
by right hand rotating through three successive space fixed simple axis rotations. Each subsequent axis of rotation is about the "space fixed" unit vectors of the parent reference frame.
Parameters ========== parent : ReferenceFrame Reference frame that this reference frame will be rotated relative to. angles : 3-tuple of sympifiable Three angles in radians used for the successive rotations. rotation_order : 3 character string or 3 digit integer Order of the rotations about the parent reference frame's unit vectors. The order can be specified by the strings ``'XZX'``, ``'131'``, or the integer ``131``. There are 12 unique valid rotation orders.
Warns ======
UserWarning If the orientation creates a kinematic loop.
Examples ========
Setup variables for the examples:
>>> from sympy import symbols >>> from sympy.physics.vector import ReferenceFrame >>> q1, q2, q3 = symbols('q1, q2, q3') >>> N = ReferenceFrame('N') >>> B = ReferenceFrame('B') >>> B1 = ReferenceFrame('B1') >>> B2 = ReferenceFrame('B2') >>> B3 = ReferenceFrame('B3')
>>> B.orient_space_fixed(N, (q1, q2, q3), '312') >>> B.dcm(N) Matrix([ [ sin(q1)*sin(q2)*sin(q3) + cos(q1)*cos(q3), sin(q1)*cos(q2), sin(q1)*sin(q2)*cos(q3) - sin(q3)*cos(q1)], [-sin(q1)*cos(q3) + sin(q2)*sin(q3)*cos(q1), cos(q1)*cos(q2), sin(q1)*sin(q3) + sin(q2)*cos(q1)*cos(q3)], [ sin(q3)*cos(q2), -sin(q2), cos(q2)*cos(q3)]])
is equivalent to:
>>> B1.orient_axis(N, N.z, q1) >>> B2.orient_axis(B1, N.x, q2) >>> B3.orient_axis(B2, N.y, q3) >>> B3.dcm(N).simplify() Matrix([ [ sin(q1)*sin(q2)*sin(q3) + cos(q1)*cos(q3), sin(q1)*cos(q2), sin(q1)*sin(q2)*cos(q3) - sin(q3)*cos(q1)], [-sin(q1)*cos(q3) + sin(q2)*sin(q3)*cos(q1), cos(q1)*cos(q2), sin(q1)*sin(q3) + sin(q2)*cos(q1)*cos(q3)], [ sin(q3)*cos(q2), -sin(q2), cos(q2)*cos(q3)]])
It is worth noting that space-fixed and body-fixed rotations are related by the order of the rotations, i.e. the reverse order of body fixed will give space fixed and vice versa.
>>> B.orient_space_fixed(N, (q1, q2, q3), '231') >>> B.dcm(N) Matrix([ [cos(q1)*cos(q2), sin(q1)*sin(q3) + sin(q2)*cos(q1)*cos(q3), -sin(q1)*cos(q3) + sin(q2)*sin(q3)*cos(q1)], [ -sin(q2), cos(q2)*cos(q3), sin(q3)*cos(q2)], [sin(q1)*cos(q2), sin(q1)*sin(q2)*cos(q3) - sin(q3)*cos(q1), sin(q1)*sin(q2)*sin(q3) + cos(q1)*cos(q3)]])
>>> B.orient_body_fixed(N, (q3, q2, q1), '132') >>> B.dcm(N) Matrix([ [cos(q1)*cos(q2), sin(q1)*sin(q3) + sin(q2)*cos(q1)*cos(q3), -sin(q1)*cos(q3) + sin(q2)*sin(q3)*cos(q1)], [ -sin(q2), cos(q2)*cos(q3), sin(q3)*cos(q2)], [sin(q1)*cos(q2), sin(q1)*sin(q2)*cos(q3) - sin(q3)*cos(q1), sin(q1)*sin(q2)*sin(q3) + cos(q1)*cos(q3)]])
"""
_check_frame(parent)
amounts = list(angles) for i, v in enumerate(amounts): if not isinstance(v, Vector): amounts[i] = sympify(v)
approved_orders = ('123', '231', '312', '132', '213', '321', '121', '131', '212', '232', '313', '323', '') # make sure XYZ => 123 rot_order = translate(str(rotation_order), 'XYZxyz', '123123') if rot_order not in approved_orders: raise TypeError('The supplied order is not an approved type') parent_orient_space = []
if not (len(amounts) == 3 & len(rot_order) == 3): raise TypeError('Space orientation takes 3 values & 3 orders') a1 = int(rot_order[0]) a2 = int(rot_order[1]) a3 = int(rot_order[2]) parent_orient_space = (self._rot(a3, amounts[2]) * self._rot(a2, amounts[1]) * self._rot(a1, amounts[0]))
self._dcm(parent, parent_orient_space)
try: from sympy.polys.polyerrors import CoercionFailed from sympy.physics.vector.functions import kinematic_equations q1, q2, q3 = amounts u1, u2, u3 = symbols('u1, u2, u3', cls=Dummy) templist = kinematic_equations([u1, u2, u3], [q1, q2, q3], 'space', rot_order) templist = [expand(i) for i in templist] td = solve(templist, [u1, u2, u3]) u1 = expand(td[u1]) u2 = expand(td[u2]) u3 = expand(td[u3]) wvec = u1 * self.x + u2 * self.y + u3 * self.z except (CoercionFailed, AssertionError): wvec = self._w_diff_dcm(parent) self._ang_vel_dict.update({parent: wvec}) parent._ang_vel_dict.update({self: -wvec}) self._var_dict = {}
def orient_quaternion(self, parent, numbers): """Sets the orientation of this reference frame relative to a parent
reference frame via an orientation quaternion. An orientation quaternion is defined as a finite rotation a unit vector, ``(lambda_x, lambda_y, lambda_z)``, by an angle ``theta``. The orientation quaternion is described by four parameters:
- ``q0 = cos(theta/2)`` - ``q1 = lambda_x*sin(theta/2)`` - ``q2 = lambda_y*sin(theta/2)`` - ``q3 = lambda_z*sin(theta/2)``
See `Quaternions and Spatial Rotation <https://en.wikipedia.org/wiki/Quaternions_and_spatial_rotation>`_ on Wikipedia for more information.
Parameters ========== parent : ReferenceFrame Reference frame that this reference frame will be rotated relative to. numbers : 4-tuple of sympifiable The four quaternion scalar numbers as defined above: ``q0``, ``q1``, ``q2``, ``q3``.
Warns ======
UserWarning If the orientation creates a kinematic loop.
Examples ========
Setup variables for the examples:
>>> from sympy import symbols >>> from sympy.physics.vector import ReferenceFrame >>> q0, q1, q2, q3 = symbols('q0 q1 q2 q3') >>> N = ReferenceFrame('N') >>> B = ReferenceFrame('B')
Set the orientation:
>>> B.orient_quaternion(N, (q0, q1, q2, q3)) >>> B.dcm(N) Matrix([ [q0**2 + q1**2 - q2**2 - q3**2, 2*q0*q3 + 2*q1*q2, -2*q0*q2 + 2*q1*q3], [ -2*q0*q3 + 2*q1*q2, q0**2 - q1**2 + q2**2 - q3**2, 2*q0*q1 + 2*q2*q3], [ 2*q0*q2 + 2*q1*q3, -2*q0*q1 + 2*q2*q3, q0**2 - q1**2 - q2**2 + q3**2]])
"""
from sympy.physics.vector.functions import dynamicsymbols _check_frame(parent)
numbers = list(numbers) for i, v in enumerate(numbers): if not isinstance(v, Vector): numbers[i] = sympify(v)
parent_orient_quaternion = [] if not (isinstance(numbers, (list, tuple)) & (len(numbers) == 4)): raise TypeError('Amounts are a list or tuple of length 4') q0, q1, q2, q3 = numbers parent_orient_quaternion = ( Matrix([[q0**2 + q1**2 - q2**2 - q3**2, 2 * (q1 * q2 - q0 * q3), 2 * (q0 * q2 + q1 * q3)], [2 * (q1 * q2 + q0 * q3), q0**2 - q1**2 + q2**2 - q3**2, 2 * (q2 * q3 - q0 * q1)], [2 * (q1 * q3 - q0 * q2), 2 * (q0 * q1 + q2 * q3), q0**2 - q1**2 - q2**2 + q3**2]]))
self._dcm(parent, parent_orient_quaternion)
t = dynamicsymbols._t q0, q1, q2, q3 = numbers q0d = diff(q0, t) q1d = diff(q1, t) q2d = diff(q2, t) q3d = diff(q3, t) w1 = 2 * (q1d * q0 + q2d * q3 - q3d * q2 - q0d * q1) w2 = 2 * (q2d * q0 + q3d * q1 - q1d * q3 - q0d * q2) w3 = 2 * (q3d * q0 + q1d * q2 - q2d * q1 - q0d * q3) wvec = Vector([(Matrix([w1, w2, w3]), self)])
self._ang_vel_dict.update({parent: wvec}) parent._ang_vel_dict.update({self: -wvec}) self._var_dict = {}
def orient(self, parent, rot_type, amounts, rot_order=''): """Sets the orientation of this reference frame relative to another
(parent) reference frame.
.. note:: It is now recommended to use the ``.orient_axis, .orient_body_fixed, .orient_space_fixed, .orient_quaternion`` methods for the different rotation types.
Parameters ==========
parent : ReferenceFrame Reference frame that this reference frame will be rotated relative to. rot_type : str The method used to generate the direction cosine matrix. Supported methods are:
- ``'Axis'``: simple rotations about a single common axis - ``'DCM'``: for setting the direction cosine matrix directly - ``'Body'``: three successive rotations about new intermediate axes, also called "Euler and Tait-Bryan angles" - ``'Space'``: three successive rotations about the parent frames' unit vectors - ``'Quaternion'``: rotations defined by four parameters which result in a singularity free direction cosine matrix
amounts : Expressions defining the rotation angles or direction cosine matrix. These must match the ``rot_type``. See examples below for details. The input types are:
- ``'Axis'``: 2-tuple (expr/sym/func, Vector) - ``'DCM'``: Matrix, shape(3,3) - ``'Body'``: 3-tuple of expressions, symbols, or functions - ``'Space'``: 3-tuple of expressions, symbols, or functions - ``'Quaternion'``: 4-tuple of expressions, symbols, or functions
rot_order : str or int, optional If applicable, the order of the successive of rotations. The string ``'123'`` and integer ``123`` are equivalent, for example. Required for ``'Body'`` and ``'Space'``.
Warns ======
UserWarning If the orientation creates a kinematic loop.
"""
_check_frame(parent)
approved_orders = ('123', '231', '312', '132', '213', '321', '121', '131', '212', '232', '313', '323', '') rot_order = translate(str(rot_order), 'XYZxyz', '123123') rot_type = rot_type.upper()
if rot_order not in approved_orders: raise TypeError('The supplied order is not an approved type')
if rot_type == 'AXIS': self.orient_axis(parent, amounts[1], amounts[0])
elif rot_type == 'DCM': self.orient_explicit(parent, amounts)
elif rot_type == 'BODY': self.orient_body_fixed(parent, amounts, rot_order)
elif rot_type == 'SPACE': self.orient_space_fixed(parent, amounts, rot_order)
elif rot_type == 'QUATERNION': self.orient_quaternion(parent, amounts)
else: raise NotImplementedError('That is not an implemented rotation')
def orientnew(self, newname, rot_type, amounts, rot_order='', variables=None, indices=None, latexs=None): r"""Returns a new reference frame oriented with respect to this
reference frame.
See ``ReferenceFrame.orient()`` for detailed examples of how to orient reference frames.
Parameters ==========
newname : str Name for the new reference frame. rot_type : str The method used to generate the direction cosine matrix. Supported methods are:
- ``'Axis'``: simple rotations about a single common axis - ``'DCM'``: for setting the direction cosine matrix directly - ``'Body'``: three successive rotations about new intermediate axes, also called "Euler and Tait-Bryan angles" - ``'Space'``: three successive rotations about the parent frames' unit vectors - ``'Quaternion'``: rotations defined by four parameters which result in a singularity free direction cosine matrix
amounts : Expressions defining the rotation angles or direction cosine matrix. These must match the ``rot_type``. See examples below for details. The input types are:
- ``'Axis'``: 2-tuple (expr/sym/func, Vector) - ``'DCM'``: Matrix, shape(3,3) - ``'Body'``: 3-tuple of expressions, symbols, or functions - ``'Space'``: 3-tuple of expressions, symbols, or functions - ``'Quaternion'``: 4-tuple of expressions, symbols, or functions
rot_order : str or int, optional If applicable, the order of the successive of rotations. The string ``'123'`` and integer ``123`` are equivalent, for example. Required for ``'Body'`` and ``'Space'``. indices : tuple of str Enables the reference frame's basis unit vectors to be accessed by Python's square bracket indexing notation using the provided three indice strings and alters the printing of the unit vectors to reflect this choice. latexs : tuple of str Alters the LaTeX printing of the reference frame's basis unit vectors to the provided three valid LaTeX strings.
Examples ========
>>> from sympy import symbols >>> from sympy.physics.vector import ReferenceFrame, vlatex >>> q0, q1, q2, q3 = symbols('q0 q1 q2 q3') >>> N = ReferenceFrame('N')
Create a new reference frame A rotated relative to N through a simple rotation.
>>> A = N.orientnew('A', 'Axis', (q0, N.x))
Create a new reference frame B rotated relative to N through body-fixed rotations.
>>> B = N.orientnew('B', 'Body', (q1, q2, q3), '123')
Create a new reference frame C rotated relative to N through a simple rotation with unique indices and LaTeX printing.
>>> C = N.orientnew('C', 'Axis', (q0, N.x), indices=('1', '2', '3'), ... latexs=(r'\hat{\mathbf{c}}_1',r'\hat{\mathbf{c}}_2', ... r'\hat{\mathbf{c}}_3')) >>> C['1'] C['1'] >>> print(vlatex(C['1'])) \hat{\mathbf{c}}_1
"""
newframe = self.__class__(newname, variables=variables, indices=indices, latexs=latexs)
approved_orders = ('123', '231', '312', '132', '213', '321', '121', '131', '212', '232', '313', '323', '') rot_order = translate(str(rot_order), 'XYZxyz', '123123') rot_type = rot_type.upper()
if rot_order not in approved_orders: raise TypeError('The supplied order is not an approved type')
if rot_type == 'AXIS': newframe.orient_axis(self, amounts[1], amounts[0])
elif rot_type == 'DCM': newframe.orient_explicit(self, amounts)
elif rot_type == 'BODY': newframe.orient_body_fixed(self, amounts, rot_order)
elif rot_type == 'SPACE': newframe.orient_space_fixed(self, amounts, rot_order)
elif rot_type == 'QUATERNION': newframe.orient_quaternion(self, amounts)
else: raise NotImplementedError('That is not an implemented rotation') return newframe
def set_ang_acc(self, otherframe, value): """Define the angular acceleration Vector in a ReferenceFrame.
Defines the angular acceleration of this ReferenceFrame, in another. Angular acceleration can be defined with respect to multiple different ReferenceFrames. Care must be taken to not create loops which are inconsistent.
Parameters ==========
otherframe : ReferenceFrame A ReferenceFrame to define the angular acceleration in value : Vector The Vector representing angular acceleration
Examples ========
>>> from sympy.physics.vector import ReferenceFrame >>> N = ReferenceFrame('N') >>> A = ReferenceFrame('A') >>> V = 10 * N.x >>> A.set_ang_acc(N, V) >>> A.ang_acc_in(N) 10*N.x
"""
if value == 0: value = Vector(0) value = _check_vector(value) _check_frame(otherframe) self._ang_acc_dict.update({otherframe: value}) otherframe._ang_acc_dict.update({self: -value})
def set_ang_vel(self, otherframe, value): """Define the angular velocity vector in a ReferenceFrame.
Defines the angular velocity of this ReferenceFrame, in another. Angular velocity can be defined with respect to multiple different ReferenceFrames. Care must be taken to not create loops which are inconsistent.
Parameters ==========
otherframe : ReferenceFrame A ReferenceFrame to define the angular velocity in value : Vector The Vector representing angular velocity
Examples ========
>>> from sympy.physics.vector import ReferenceFrame >>> N = ReferenceFrame('N') >>> A = ReferenceFrame('A') >>> V = 10 * N.x >>> A.set_ang_vel(N, V) >>> A.ang_vel_in(N) 10*N.x
"""
if value == 0: value = Vector(0) value = _check_vector(value) _check_frame(otherframe) self._ang_vel_dict.update({otherframe: value}) otherframe._ang_vel_dict.update({self: -value})
@property def x(self): """The basis Vector for the ReferenceFrame, in the x direction. """ return self._x
@property def y(self): """The basis Vector for the ReferenceFrame, in the y direction. """ return self._y
@property def z(self): """The basis Vector for the ReferenceFrame, in the z direction. """ return self._z
def partial_velocity(self, frame, *gen_speeds): """Returns the partial angular velocities of this frame in the given
frame with respect to one or more provided generalized speeds.
Parameters ========== frame : ReferenceFrame The frame with which the angular velocity is defined in. gen_speeds : functions of time The generalized speeds.
Returns ======= partial_velocities : tuple of Vector The partial angular velocity vectors corresponding to the provided generalized speeds.
Examples ========
>>> from sympy.physics.vector import ReferenceFrame, dynamicsymbols >>> N = ReferenceFrame('N') >>> A = ReferenceFrame('A') >>> u1, u2 = dynamicsymbols('u1, u2') >>> A.set_ang_vel(N, u1 * A.x + u2 * N.y) >>> A.partial_velocity(N, u1) A.x >>> A.partial_velocity(N, u1, u2) (A.x, N.y)
"""
partials = [self.ang_vel_in(frame).diff(speed, frame, var_in_dcm=False) for speed in gen_speeds]
if len(partials) == 1: return partials[0] else: return tuple(partials)
def _check_frame(other): from .vector import VectorTypeError if not isinstance(other, ReferenceFrame): raise VectorTypeError(other, ReferenceFrame('A'))
|
