78 lines
2.6 KiB
Python
78 lines
2.6 KiB
Python
from sympy import symbols
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from sympy.physics.mechanics import Point, Particle, ReferenceFrame, inertia
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from sympy.physics.mechanics.body_base import BodyBase
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from sympy.testing.pytest import raises, warns_deprecated_sympy
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def test_particle_default():
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# Test default
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p = Particle('P')
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assert p.name == 'P'
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assert p.mass == symbols('P_mass')
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assert p.masscenter.name == 'P_masscenter'
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assert p.potential_energy == 0
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assert p.__str__() == 'P'
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assert p.__repr__() == ("Particle('P', masscenter=P_masscenter, "
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"mass=P_mass)")
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raises(AttributeError, lambda: p.frame)
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def test_particle():
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# Test initializing with parameters
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m, m2, v1, v2, v3, r, g, h = symbols('m m2 v1 v2 v3 r g h')
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P = Point('P')
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P2 = Point('P2')
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p = Particle('pa', P, m)
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assert isinstance(p, BodyBase)
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assert p.mass == m
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assert p.point == P
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# Test the mass setter
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p.mass = m2
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assert p.mass == m2
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# Test the point setter
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p.point = P2
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assert p.point == P2
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# Test the linear momentum function
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N = ReferenceFrame('N')
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O = Point('O')
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P2.set_pos(O, r * N.y)
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P2.set_vel(N, v1 * N.x)
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raises(TypeError, lambda: Particle(P, P, m))
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raises(TypeError, lambda: Particle('pa', m, m))
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assert p.linear_momentum(N) == m2 * v1 * N.x
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assert p.angular_momentum(O, N) == -m2 * r * v1 * N.z
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P2.set_vel(N, v2 * N.y)
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assert p.linear_momentum(N) == m2 * v2 * N.y
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assert p.angular_momentum(O, N) == 0
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P2.set_vel(N, v3 * N.z)
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assert p.linear_momentum(N) == m2 * v3 * N.z
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assert p.angular_momentum(O, N) == m2 * r * v3 * N.x
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P2.set_vel(N, v1 * N.x + v2 * N.y + v3 * N.z)
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assert p.linear_momentum(N) == m2 * (v1 * N.x + v2 * N.y + v3 * N.z)
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assert p.angular_momentum(O, N) == m2 * r * (v3 * N.x - v1 * N.z)
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p.potential_energy = m * g * h
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assert p.potential_energy == m * g * h
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# TODO make the result not be system-dependent
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assert p.kinetic_energy(
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N) in [m2 * (v1 ** 2 + v2 ** 2 + v3 ** 2) / 2,
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m2 * v1 ** 2 / 2 + m2 * v2 ** 2 / 2 + m2 * v3 ** 2 / 2]
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def test_parallel_axis():
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N = ReferenceFrame('N')
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m, a, b = symbols('m, a, b')
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o = Point('o')
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p = o.locatenew('p', a * N.x + b * N.y)
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P = Particle('P', o, m)
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Ip = P.parallel_axis(p, N)
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Ip_expected = inertia(N, m * b ** 2, m * a ** 2, m * (a ** 2 + b ** 2),
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ixy=-m * a * b)
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assert Ip == Ip_expected
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def test_deprecated_set_potential_energy():
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m, g, h = symbols('m g h')
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P = Point('P')
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p = Particle('pa', P, m)
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with warns_deprecated_sympy():
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p.set_potential_energy(m * g * h)
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