Visualize.py

#!/usr/bin/env python

from matplotlib import pyplot as plt
from matplotlib import animation


class Particle:

    def __init__(self, x, y, ang_speed):
        self.x = x
        self.y = y
        self.ang_speed = ang_speed


class ParticleSimulator:

    def __init__(self, particles):
        self.particles = particles

    def evolve(self, dt):
        timestep = 0.00001
        nsteps = int(dt / timestep)

        for i in range(nsteps):
            for p in self.particles:

                # 1. calculate the direction
                norm = (p.x ** 2 + p.y ** 2) ** 0.5
                v_x = (-p.y) / norm
                v_y = p.x / norm

                # 2. calculate the displacement
                d_x = timestep * p.ang_speed * v_x
                d_y = timestep * p.ang_speed * v_y

                p.x += d_x
                p.y += d_y

                # 3. repeat for all the time steps


def visualize(simulator):
    X = [p.x for p in simulator.particles]
    Y = [p.y for p in simulator.particles]

    fig = plt.figure()
    ax = plt.subplot(111, aspect='equal')
    line, = ax.plot(X, Y, 'ro')

    # Axis limits
    plt.xlim(-1, 1)
    plt.ylim(-1, 1)

    # It will be run when the animation starts
    def init():
        line.set_data([], [])
        return line,

    def animate(i):
        # We let the particle evolve for 0.1 time units
        simulator.evolve(0.01)
        X = [p.x for p in simulator.particles]
        Y = [p.y for p in simulator.particles]

        line.set_data(X, Y)
        return line,

    # Call the animate function each 10 ms
    anim = animation.FuncAnimation(fig, animate,
                                   init_func=init,
                                   blit=True,
                                   # Efficient animation
                                   interval=10)
    plt.show()

    def test_visualize():
        particles = [Particle(0.3,  0.5,  +1),
                     Particle(0.0,  -0.5, -1),
                     Particle(-0.1, -0.4, +3)]

        simulator = ParticleSimulator(particles)
        visualize(simulator)

    if __name__ == '__main__':
        test_visualize()