Scipy.integrate.ode Gives Up On Integration

I am encountering a strange problem with scipy.integrate.ode. Here is a minimal working example: import sys import time import numpy as np import matplotlib.pyplot as plt import ma

Solution 1:

"My current suspicion is that the integrator decided that my function is constant after it did not change significantly during the first few integration steps." Your suspicion is correct. ODE solvers typically have an internal step size that is adaptively adjusted based on error estimates computed by the solver. These step sizes are independent of the times for which the output is requested; the output at the requested times is computed using interpolation of the solution at the points computed at the internal steps.

When you start your solver at t = -20, apparently the input changes so slowly that the solver's internal step size becomes large enough that by the time the solver gets near t = 0, the solver skips right over the input pulse.

You can limit the internal step size with the option max_step of the set_integrator method. If I set max_step to 2.0 (for example),

r = ode(ode_fun).set_integrator('zvode', method='adams', with_jacobian=False,
                                max_step=2.0)

I get the output that you expect.