textbook example code: lagrange_points.pyΒΆ

[source code]

import numpy
from matplotlib import pyplot
from amuse.plot import xlabel, ylabel, effective_iso_potential_plot
from amuse.units import units, constants, nbody_system
from amuse.community.hermite0.interface import Hermite
from amuse.datamodel import Particles

def new_sun_earth_system():
    particles = Particles(2)
    particles.mass = [1, 0.2] | units.MSun
    particles.position = [[0, 0, 0], [1.0, 0, 0]] | units.AU
    particles.velocity = [0, 0, 0] | units.km / units.s
    particles[1].vy = (constants.G * particles.total_mass()
                        / particles[1].x).sqrt()
    return particles

def setup_gravity_code():
    converter = nbody_system.nbody_to_si(1.0|units.MSun, 1.0|units.AU)
    gravity = Hermite(converter)
    gravity.particles.add_particles(new_sun_earth_system())
    return gravity

def make_effective_iso_potential_plot(gravity_code):
    omega = (constants.G * gravity_code.particles.total_mass()
              / (1.0|units.AU**3)).sqrt()
    center_of_mass = gravity_code.particles.center_of_mass()[:2]

    pyplot.rcParams.update({'font.size': 30})
    figure = pyplot.figure(figsize = (12, 12))
    ax = pyplot.gca()
    ax.get_yaxis().get_major_formatter().set_useOffset(False)
    ax.minorticks_on()

    current_axes = pyplot.subplot(1, 1, 1)
    current_axes.set_aspect("equal", adjustable = "box")
    lim = 1.7
    effective_iso_potential_plot(gravity_code,
                                 omega,
                                 xlim = [-lim, lim] | units.AU,
                                 ylim = [-lim, lim] | units.AU,
                                 center_of_rotation = center_of_mass,
                                 fraction_screen_filled=0.8)
    xlabel('x')
    ylabel('y')
    pyplot.text(0.6, -0.06, "$L_1$")
    pyplot.text(1.35, -0.06, "$L_2$")
    pyplot.text(-0.99, -0.06, "$L_3$")
    pyplot.text(0.40, 0.82, "$L_4$")
    pyplot.text(0.40, -0.92, "$L_5$")

    save_file = 'lagrange_points.png'
    pyplot.savefig(save_file)
    print "\nOutput saved in", save_file
    pyplot.show()

if __name__ == "__main__":
    gravity = setup_gravity_code()
    make_effective_iso_potential_plot(gravity)
    gravity.stop()

Keywords: python, amuse, astrophysics, matplotlib, pylab, example, codex (see how-to-search-examples)