def test21(self):
particles = datamodel.Particles(2)
particles.x = [0.0,10.0] | nbody_system.length
particles.y = 0.0 | nbody_system.length
particles.z = 0.0 | nbody_system.length
particles.radius = 0.005 | nbody_system.length
particles.vx = 0.0 | nbody_system.speed
particles.vy = 0.0 | nbody_system.speed
particles.vz = 0.0 | nbody_system.speed
particles.mass = 1.0 | nbody_system.mass
very_short_time_to_evolve = 1 | units.s
very_long_time_to_evolve = 1e9 | nbody_system.time
instance = FDPS()
instance.initialize_code()
instance.parameters.epsilon_squared = (1e-5 | nbody_system.length)**2
instance.particles.add_particles(particles)
instance.commit_particles()
self.assertAlmostRelativeEquals(instance.potential_energy, -0.1 | nbody_system.energy, 5)
instance.stop()
def test15(self):
print "Test15: Testing effect of FDPS parameter epsilon_squared"
convert_nbody = nbody_system.nbody_to_si(1.0 | units.MSun, 1.0 | units.AU)
particles = datamodel.Particles(2)
sun = particles[0]
sun.mass = 1.0 | units.MSun
sun.position = [0.0, 0.0, 0.0] | units.AU
sun.velocity = [0.0, 0.0, 0.0] | units.AU / units.yr
sun.radius = 1.0 | units.RSun
earth = particles[1]
earth.mass = 5.9736e24 | units.kg
earth.radius = 6371.0 | units.km
earth.position = [0.0, 1.0, 0.0] | units.AU
earth.velocity = [2.0*numpy.pi, -0.0001, 0.0] | units.AU / units.yr
initial_direction = math.atan((earth.velocity[0]/earth.velocity[1]))
final_direction = []
for log_eps2 in range(-9,10,2):
instance = FDPS(convert_nbody)
instance.initialize_code()
instance.parameters.epsilon_squared = 10.0**log_eps2 | units.AU ** 2
instance.parameters.timestep = 0.005 | units.yr
instance.particles.add_particles(particles)
instance.commit_particles()
instance.evolve_model(0.25 | units.yr)
final_direction.append(math.atan((instance.particles[1].velocity[0]/
instance.particles[1].velocity[1])))
instance.stop()
# Small values of epsilon_squared should result in normal earth-sun dynamics: rotation of 90 degrees
self.assertAlmostEquals(abs(final_direction[0]), abs(initial_direction+math.pi/2.0), 2)
# Large values of epsilon_squared should result in ~ no interaction
self.assertAlmostEquals(final_direction[-1], initial_direction, 2)
# Outcome is most sensitive to epsilon_squared when epsilon_squared = d(earth, sun)^2
delta = [abs(final_direction[i+1]-final_direction[i]) for i in range(len(final_direction)-1)]
self.assertEquals(delta[len(final_direction)//2 -1], max(delta))
def test16(self):
numpy.random.seed(0)
number_of_stars = 2
stars = plummer.new_plummer_model(number_of_stars)
stars.radius = 0.00001 | nbody_system.length
stars.scale_to_standard()
instance = FDPS()
instance.initialize_code()
instance.parameters.epsilon_squared = (1.0 / 20.0 / (number_of_stars**0.33333) | nbody_system.length)**2
instance.parameters.timestep = 0.004 | nbody_system.time
instance.parameters.timestep = 0.00001 | nbody_system.time
instance.commit_parameters()
print instance.parameters.timestep
instance.particles.add_particles(stars)
instance.commit_particles()
energy_total_t0 = instance.potential_energy + instance.kinetic_energy
request = instance.evolve_model.async(1.0 | nbody_system.time)
request.result()
energy_total_t1 = instance.potential_energy + instance.kinetic_energy
self.assertAlmostRelativeEqual(energy_total_t0, energy_total_t1, 3)
instance.stop()
numpy.random.seed()