Source code for sympy.physics.mechanics.functions

from __future__ import print_function, division
import warnings

from sympy.utilities.exceptions import SymPyDeprecationWarning
from sympy.utilities.misc import filldedent
from sympy.physics.vector import Vector, ReferenceFrame, Point
from sympy.physics.vector.printing import (vprint, vsprint, vpprint, vlatex,
                                           init_vprinting)
from sympy.physics.mechanics.particle import Particle
from sympy.physics.mechanics.rigidbody import RigidBody
from sympy import sympify
from sympy.core.basic import S

__all__ = ['inertia',
           'inertia_of_point_mass',
           'linear_momentum',
           'angular_momentum',
           'kinetic_energy',
           'potential_energy',
           'Lagrangian',
           'mechanics_printing',
           'mprint',
           'msprint',
           'mpprint',
           'mlatex']

warnings.simplefilter("always", SymPyDeprecationWarning)

# These are functions that we've moved and renamed during extracting the
# basic vector calculus code from the mechanics packages.

mprint = vprint
msprint = vsprint
mpprint = vpprint
mlatex = vlatex


def mechanics_printing(**kwargs):

    # mechanics_printing has slightly different functionality in 0.7.5 but
    # shouldn't fundamentally need a deprecation warning so we do this
    # little wrapper that gives the warning that things have changed.

    # TODO : Remove this warning in the release after SymPy 0.7.5

    # The message is only printed if this function is called with no args,
    # as was the previous only way to call it.

    def dict_is_empty(D):
        for k in D:
            return False
        return True

    if dict_is_empty(kwargs):
        msg = ('See the doc string for slight changes to this function: '
               'keyword args may be needed for the desired effect. '
               'Otherwise use sympy.physics.vector.init_vprinting directly.')
        SymPyDeprecationWarning(filldedent(msg)).warn()

    init_vprinting(**kwargs)

mechanics_printing.__doc__ = init_vprinting.__doc__


[docs]def inertia(frame, ixx, iyy, izz, ixy=0, iyz=0, izx=0): """Simple way to create inertia Dyadic object. If you don't know what a Dyadic is, just treat this like the inertia tensor. Then, do the easy thing and define it in a body-fixed frame. Parameters ========== frame : ReferenceFrame The frame the inertia is defined in ixx : Sympifyable the xx element in the inertia dyadic iyy : Sympifyable the yy element in the inertia dyadic izz : Sympifyable the zz element in the inertia dyadic ixy : Sympifyable the xy element in the inertia dyadic iyz : Sympifyable the yz element in the inertia dyadic izx : Sympifyable the zx element in the inertia dyadic Examples ======== >>> from sympy.physics.mechanics import ReferenceFrame, inertia >>> N = ReferenceFrame('N') >>> inertia(N, 1, 2, 3) (N.x|N.x) + 2*(N.y|N.y) + 3*(N.z|N.z) """ if not isinstance(frame, ReferenceFrame): raise TypeError('Need to define the inertia in a frame') ol = sympify(ixx) * (frame.x | frame.x) ol += sympify(ixy) * (frame.x | frame.y) ol += sympify(izx) * (frame.x | frame.z) ol += sympify(ixy) * (frame.y | frame.x) ol += sympify(iyy) * (frame.y | frame.y) ol += sympify(iyz) * (frame.y | frame.z) ol += sympify(izx) * (frame.z | frame.x) ol += sympify(iyz) * (frame.z | frame.y) ol += sympify(izz) * (frame.z | frame.z) return ol
[docs]def inertia_of_point_mass(mass, pos_vec, frame): """Inertia dyadic of a point mass realtive to point O. Parameters ========== mass : Sympifyable Mass of the point mass pos_vec : Vector Position from point O to point mass frame : ReferenceFrame Reference frame to express the dyadic in Examples ======== >>> from sympy import symbols >>> from sympy.physics.mechanics import ReferenceFrame, inertia_of_point_mass >>> N = ReferenceFrame('N') >>> r, m = symbols('r m') >>> px = r * N.x >>> inertia_of_point_mass(m, px, N) m*r**2*(N.y|N.y) + m*r**2*(N.z|N.z) """ return mass * (((frame.x | frame.x) + (frame.y | frame.y) + (frame.z | frame.z)) * (pos_vec & pos_vec) - (pos_vec | pos_vec))
[docs]def linear_momentum(frame, *body): """Linear momentum of the system. This function returns the linear momentum of a system of Particle's and/or RigidBody's. The linear momentum of a system is equal to the vector sum of the linear momentum of its constituents. Consider a system, S, comprised of a rigid body, A, and a particle, P. The linear momentum of the system, L, is equal to the vector sum of the linear momentum of the particle, L1, and the linear momentum of the rigid body, L2, i.e- L = L1 + L2 Parameters ========== frame : ReferenceFrame The frame in which linear momentum is desired. body1, body2, body3... : Particle and/or RigidBody The body (or bodies) whose kinetic energy is required. Examples ======== >>> from sympy.physics.mechanics import Point, Particle, ReferenceFrame >>> from sympy.physics.mechanics import RigidBody, outer, linear_momentum >>> N = ReferenceFrame('N') >>> P = Point('P') >>> P.set_vel(N, 10 * N.x) >>> Pa = Particle('Pa', P, 1) >>> Ac = Point('Ac') >>> Ac.set_vel(N, 25 * N.y) >>> I = outer(N.x, N.x) >>> A = RigidBody('A', Ac, N, 20, (I, Ac)) >>> linear_momentum(N, A, Pa) 10*N.x + 500*N.y """ if not isinstance(frame, ReferenceFrame): raise TypeError('Please specify a valid ReferenceFrame') else: linear_momentum_sys = Vector(0) for e in body: if isinstance(e, (RigidBody, Particle)): linear_momentum_sys += e.linear_momentum(frame) else: raise TypeError('*body must have only Particle or RigidBody') return linear_momentum_sys
[docs]def angular_momentum(point, frame, *body): """Angular momentum of a system This function returns the angular momentum of a system of Particle's and/or RigidBody's. The angular momentum of such a system is equal to the vector sum of the angular momentum of its constituents. Consider a system, S, comprised of a rigid body, A, and a particle, P. The angular momentum of the system, H, is equal to the vector sum of the linear momentum of the particle, H1, and the linear momentum of the rigid body, H2, i.e- H = H1 + H2 Parameters ========== point : Point The point about which angular momentum of the system is desired. frame : ReferenceFrame The frame in which angular momentum is desired. body1, body2, body3... : Particle and/or RigidBody The body (or bodies) whose kinetic energy is required. Examples ======== >>> from sympy.physics.mechanics import Point, Particle, ReferenceFrame >>> from sympy.physics.mechanics import RigidBody, outer, angular_momentum >>> N = ReferenceFrame('N') >>> O = Point('O') >>> O.set_vel(N, 0 * N.x) >>> P = O.locatenew('P', 1 * N.x) >>> P.set_vel(N, 10 * N.x) >>> Pa = Particle('Pa', P, 1) >>> Ac = O.locatenew('Ac', 2 * N.y) >>> Ac.set_vel(N, 5 * N.y) >>> a = ReferenceFrame('a') >>> a.set_ang_vel(N, 10 * N.z) >>> I = outer(N.z, N.z) >>> A = RigidBody('A', Ac, a, 20, (I, Ac)) >>> angular_momentum(O, N, Pa, A) 10*N.z """ if not isinstance(frame, ReferenceFrame): raise TypeError('Please enter a valid ReferenceFrame') if not isinstance(point, Point): raise TypeError('Please specify a valid Point') else: angular_momentum_sys = Vector(0) for e in body: if isinstance(e, (RigidBody, Particle)): angular_momentum_sys += e.angular_momentum(point, frame) else: raise TypeError('*body must have only Particle or RigidBody') return angular_momentum_sys
[docs]def kinetic_energy(frame, *body): """Kinetic energy of a multibody system. This function returns the kinetic energy of a system of Particle's and/or RigidBody's. The kinetic energy of such a system is equal to the sum of the kinetic energies of its constituents. Consider a system, S, comprising a rigid body, A, and a particle, P. The kinetic energy of the system, T, is equal to the vector sum of the kinetic energy of the particle, T1, and the kinetic energy of the rigid body, T2, i.e. T = T1 + T2 Kinetic energy is a scalar. Parameters ========== frame : ReferenceFrame The frame in which the velocity or angular velocity of the body is defined. body1, body2, body3... : Particle and/or RigidBody The body (or bodies) whose kinetic energy is required. Examples ======== >>> from sympy.physics.mechanics import Point, Particle, ReferenceFrame >>> from sympy.physics.mechanics import RigidBody, outer, kinetic_energy >>> N = ReferenceFrame('N') >>> O = Point('O') >>> O.set_vel(N, 0 * N.x) >>> P = O.locatenew('P', 1 * N.x) >>> P.set_vel(N, 10 * N.x) >>> Pa = Particle('Pa', P, 1) >>> Ac = O.locatenew('Ac', 2 * N.y) >>> Ac.set_vel(N, 5 * N.y) >>> a = ReferenceFrame('a') >>> a.set_ang_vel(N, 10 * N.z) >>> I = outer(N.z, N.z) >>> A = RigidBody('A', Ac, a, 20, (I, Ac)) >>> kinetic_energy(N, Pa, A) 350 """ if not isinstance(frame, ReferenceFrame): raise TypeError('Please enter a valid ReferenceFrame') ke_sys = S(0) for e in body: if isinstance(e, (RigidBody, Particle)): ke_sys += e.kinetic_energy(frame) else: raise TypeError('*body must have only Particle or RigidBody') return ke_sys
[docs]def potential_energy(*body): """Potential energy of a multibody system. This function returns the potential energy of a system of Particle's and/or RigidBody's. The potential energy of such a system is equal to the sum of the potential energy of its constituents. Consider a system, S, comprising a rigid body, A, and a particle, P. The potential energy of the system, V, is equal to the vector sum of the potential energy of the particle, V1, and the potential energy of the rigid body, V2, i.e. V = V1 + V2 Potential energy is a scalar. Parameters ========== body1, body2, body3... : Particle and/or RigidBody The body (or bodies) whose potential energy is required. Examples ======== >>> from sympy.physics.mechanics import Point, Particle, ReferenceFrame >>> from sympy.physics.mechanics import RigidBody, outer, potential_energy >>> from sympy import symbols >>> M, m, g, h = symbols('M m g h') >>> N = ReferenceFrame('N') >>> O = Point('O') >>> O.set_vel(N, 0 * N.x) >>> P = O.locatenew('P', 1 * N.x) >>> Pa = Particle('Pa', P, m) >>> Ac = O.locatenew('Ac', 2 * N.y) >>> a = ReferenceFrame('a') >>> I = outer(N.z, N.z) >>> A = RigidBody('A', Ac, a, M, (I, Ac)) >>> Pa.set_potential_energy(m * g * h) >>> A.set_potential_energy(M * g * h) >>> potential_energy(Pa, A) M*g*h + g*h*m """ pe_sys = S(0) for e in body: if isinstance(e, (RigidBody, Particle)): pe_sys += e.potential_energy else: raise TypeError('*body must have only Particle or RigidBody') return pe_sys
[docs]def Lagrangian(frame, *body): """Lagrangian of a multibody system. This function returns the Lagrangian of a system of Particle's and/or RigidBody's. The Lagrangian of such a system is equal to the difference between the kinetic energies and potential energies of its constituents. If T and V are the kinetic and potential energies of a system then it's Lagrangian, L, is defined as L = T - V The Lagrangian is a scalar. Parameters ========== frame : ReferenceFrame The frame in which the velocity or angular velocity of the body is defined to determine the kinetic energy. body1, body2, body3... : Particle and/or RigidBody The body (or bodies) whose kinetic energy is required. Examples ======== >>> from sympy.physics.mechanics import Point, Particle, ReferenceFrame >>> from sympy.physics.mechanics import RigidBody, outer, Lagrangian >>> from sympy import symbols >>> M, m, g, h = symbols('M m g h') >>> N = ReferenceFrame('N') >>> O = Point('O') >>> O.set_vel(N, 0 * N.x) >>> P = O.locatenew('P', 1 * N.x) >>> P.set_vel(N, 10 * N.x) >>> Pa = Particle('Pa', P, 1) >>> Ac = O.locatenew('Ac', 2 * N.y) >>> Ac.set_vel(N, 5 * N.y) >>> a = ReferenceFrame('a') >>> a.set_ang_vel(N, 10 * N.z) >>> I = outer(N.z, N.z) >>> A = RigidBody('A', Ac, a, 20, (I, Ac)) >>> Pa.set_potential_energy(m * g * h) >>> A.set_potential_energy(M * g * h) >>> Lagrangian(N, Pa, A) -M*g*h - g*h*m + 350 """ if not isinstance(frame, ReferenceFrame): raise TypeError('Please supply a valid ReferenceFrame') for e in body: if not isinstance(e, (RigidBody, Particle)): raise TypeError('*body must have only Particle or RigidBody') return kinetic_energy(frame, *body) - potential_energy(*body)