.. _animation-double_pendulum_animated: animation example code: double_pendulum_animated.py =================================================== [`source code `_] :: # Double pendulum formula translated from the C code at # http://www.physics.usyd.edu.au/~wheat/dpend_html/solve_dpend.c from numpy import sin, cos, pi, array import numpy as np import matplotlib.pyplot as plt import scipy.integrate as integrate import matplotlib.animation as animation G = 9.8 # acceleration due to gravity, in m/s^2 L1 = 1.0 # length of pendulum 1 in m L2 = 1.0 # length of pendulum 2 in m M1 = 1.0 # mass of pendulum 1 in kg M2 = 1.0 # mass of pendulum 2 in kg def derivs(state, t): dydx = np.zeros_like(state) dydx[0] = state[1] del_ = state[2]-state[0] den1 = (M1+M2)*L1 - M2*L1*cos(del_)*cos(del_) dydx[1] = (M2*L1*state[1]*state[1]*sin(del_)*cos(del_) + M2*G*sin(state[2])*cos(del_) + M2*L2*state[3]*state[3]*sin(del_) - (M1+M2)*G*sin(state[0]))/den1 dydx[2] = state[3] den2 = (L2/L1)*den1 dydx[3] = (-M2*L2*state[3]*state[3]*sin(del_)*cos(del_) + (M1+M2)*G*sin(state[0])*cos(del_) - (M1+M2)*L1*state[1]*state[1]*sin(del_) - (M1+M2)*G*sin(state[2]))/den2 return dydx # create a time array from 0..100 sampled at 0.1 second steps dt = 0.05 t = np.arange(0.0, 20, dt) # th1 and th2 are the initial angles (degrees) # w10 and w20 are the initial angular velocities (degrees per second) th1 = 120.0 w1 = 0.0 th2 = -10.0 w2 = 0.0 rad = pi/180 # initial state state = np.array([th1, w1, th2, w2])*pi/180. # integrate your ODE using scipy.integrate. y = integrate.odeint(derivs, state, t) x1 = L1*sin(y[:,0]) y1 = -L1*cos(y[:,0]) x2 = L2*sin(y[:,2]) + x1 y2 = -L2*cos(y[:,2]) + y1 fig = plt.figure() ax = fig.add_subplot(111, autoscale_on=False, xlim=(-2, 2), ylim=(-2, 2)) ax.grid() line, = ax.plot([], [], 'o-', lw=2) time_template = 'time = %.1fs' time_text = ax.text(0.05, 0.9, '', transform=ax.transAxes) def init(): line.set_data([], []) time_text.set_text('') return line, time_text def animate(i): thisx = [0, x1[i], x2[i]] thisy = [0, y1[i], y2[i]] line.set_data(thisx, thisy) time_text.set_text(time_template%(i*dt)) return line, time_text ani = animation.FuncAnimation(fig, animate, np.arange(1, len(y)), interval=25, blit=True, init_func=init) #ani.save('double_pendulum.mp4', fps=15, clear_temp=True) plt.show() Keywords: python, matplotlib, pylab, example, codex (see :ref:`how-to-search-examples`)