# apps121025_test_liouville.app02_setup¶

A simple setup. Refactoring of app01

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. Refactoring of app01

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 kep_particle(pos, vel):
''' Kepler's particle simulation for a specific particle
'''
### Set the mass (center).  Assume Jupiter (roughly).
ms = 2e27 # kg

### Instance the kepler class
#    kep = kepler.Kepler2RungeKutta(ms, 1., pos, vel)
kep = kepler.KeplerRungeKutta(ms, 1., pos, vel)

### Trace the particle along the time.
tlist = [0, 3e4]

posvel = kep.get_posvel(tlist)
return posvel[-1, :3], posvel[-1, 3:]

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

### Set the particle velocity. Assume 10 km/s at 60 deg inward from x.
inivel = np.array([-10e3 * 0.5, 10e3 * np.sqrt(3./4), 0])

pos1, vel1 = kep_particle(inipos, inivel)

plt.figure()
plt.plot(inipos, inipos, 'o')
plt.plot(pos1, pos1, 'o')
plt.gca().set_aspect('equal')

plt.savefig('app02_setup.png')

if __name__ == "__main__":
main()