apps121025_test_liouville.app01_setup

A simple setup.

Set a massive star in the center. Set a particle (reference) at the arbitrary position. Set a particle velocity (reference) at

To eliminate the problem into 2D x 2D for the first step, the particle position is on x-axis and the velocity has only vx, vy components.

''' A simple setup.

Set a massive star in the center.
Set a particle (reference) at the arbitrary position.
Set a particle velocity (reference) at 

To eliminate the problem into 2D x 2D for the first step,
the particle position is on x-axis and the velocity
has only vx, vy components.
'''

import numpy as np
import matplotlib.pyplot as plt

import irfpy.util.keplernumeric as kepler

def main():
    ### Set the mass (center).  Assume Jupiter (roughly).
    ms = 2e27 # kg

    ### Set the particle position. Assume Io position.
    pos = np.array([4.5e8, 0, 0])  # m

    ### Set the particle velocity. Assume 10 km/s at 60 deg inward from x.
    vel = np.array([-10e3 * 0.5, 10e3 * np.sqrt(3./4), 0])
    
    ### Instance the kepler class
    kep = kepler.Kepler2RungeKutta(ms, 1., pos, vel)

    ### Trace the particle along the time.
    tlist = np.arange(0, 3e4, 60)
    print(len(tlist))

    posvel = kep.get_posvel(tlist)

    plt.figure()
    plt.subplot(211)
    plt.plot(posvel[:, 0], posvel[:, 1])
    plt.subplot(212)
    plt.plot(posvel[:, 3], posvel[:, 4])
    plt.gca().set_aspect('equal')

    plt.savefig('app01_setup.png')

if __name__ == "__main__":
    main()