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Minor cleanup to double_pendulum example. #12986

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Dec 13, 2018
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Minor cleanup to double_pendulum example. #12986

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30 changes: 16 additions & 14 deletions examples/animation/double_pendulum_sgskip.py
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Original file line number Diff line number Diff line change
Expand Up @@ -27,26 +27,28 @@ 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
delta = state[2] - state[0]
den1 = (M1+M2) * L1 - M2 * L1 * cos(delta) * cos(delta)
dydx[1] = ((M2 * L1 * state[1] * state[1] * sin(delta) * cos(delta)
+ M2 * G * sin(state[2]) * cos(delta)
+ M2 * L2 * state[3] * state[3] * sin(delta)
- (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
den2 = (L2/L1) * den1
dydx[3] = ((- M2 * L2 * state[3] * state[3] * sin(delta) * cos(delta)
+ (M1+M2) * G * sin(state[0]) * cos(delta)
- (M1+M2) * L1 * state[1] * state[1] * sin(delta)
- (M1+M2) * G * sin(state[2]))
/ den2)

return dydx

# create a time array from 0..100 sampled at 0.05 second steps
dt = 0.05
t = np.arange(0.0, 20, dt)
t = np.arange(0, 20, dt)

# th1 and th2 are the initial angles (degrees)
# w10 and w20 are the initial angular velocities (degrees per second)
Expand Down Expand Up @@ -91,7 +93,7 @@ def animate(i):
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 = animation.FuncAnimation(fig, animate, range(1, len(y)),
interval=25, blit=True, init_func=init)
plt.show()