[SciPy-User] strange behavior calling odeint from brentq

Schmidt, Phil PSchmidt@watlow....
Tue Nov 22 14:11:06 CST 2011


I am implementing the shooting method using optimize.brentq() and integrate.odeint(). The following is an outline of my code:

def objective(t2, *args):
    t1 = args[0]
    x_init = args[1]
    x_target = args[2]
    x = odeint(dxdt, x_init, [t1, t2])
    return x - x_target

t_target = brentq(objective, t1, t2, args=(t1, x_init, x_target))

I have observed that if I place do-nothing statements in the objective function (e.g., print statements or dummy assignments like t1=t1), sometimes I will get different answers for t_target. I have not identified a pattern for when this may or may not occur, but presumably there is some dependency between brentq() and odeint().

I am running Scipy 0.9.0rc3, Python 2.6.5, Windows XP.

Can anyone explain why this is happening, and point me to the "right" way to do what I'm attemtping?


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