parabolic_collision.py

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## @file parabolic_collision.py Testing collision detection module by putting planets on a parabolic orbit.
from common import *
from math import sqrt
def norm(*args):
    return sqrt(sum(x * x for x in args))

class ParabolicTest(abstract.IntegrationTest):
    """
    collision happens at exactly t= 1.885638833885 for nbod=3
    """
    cfg = swarmng.config(
            integrator = "hermite_cpu",
            time_step  = 1e-3,
            nogpu      = 1,
            )
    destination_time = 1.885638833885

    def createEnsemble(self):
        nsys = 16
        nbod = 3
        R = 1
        mu = 1
        mass_planet = 0.0001


        ens = swarmng.DefaultEnsemble.create(nbod,nsys)
        for s in ens:
            s.time = 0
            s.id = 0
            s.state = 0
            s[0].pos = [ 0, 0, 0 ]
            s[0].vel = [ 0, 0, 0 ]
            s[0].mass = 1
            for j in range(1,ens.nbod):
                x = ((j % 2)*2-1)*2*((j+1)/2)
                y = x * x / 4 / R - R
                vmag = sqrt(2*mu/norm(x,y))
                vdirx = (x/abs(x))/norm(1,x/2/R)
                vdiry = abs(x)/2/R / norm(1,x/2/R)
                s[j].pos = [ x, y, 0 ]
                s[j].vel = [ -vmag*vdirx, -vmag*vdiry, 0 ]
                s[j].mass = mass_planet
        return ens


    def examine(self):
        rs = self.ref[0]
        s = self.ens[0]
        print rs[1].pos, rs[2].pos, rs[1].vel, rs[2].vel
        print s[1].pos, s[2].pos

        x1,y1,z1 = s[1].pos
        x2,y2,z2 = s[2].pos
        self.assertAlmostEqual(norm(x2-x1,y2-y1,z2-z1),0)