[SciPy-User] multiple ODE problem with scipy.integrate.ode.ode

[Vitor Matos]

Hi,
I've been trying to perform the integration of multiple ODEs.

The problem is that only the first ODE being integrated produces the
correct solution. The subsequent ODE solution come out as gibberish.

To demonstrate the problem, I've written a simple code that solves two
RC circuit ODEs:

----------------------------------------------------------------------

from scipy.integrate import *

def f(t, y, arg1):
    # dV/dt = -1/RC (V - Vi)
    return -1/(arg1[0]*arg1[1])*(y - arg1[2])

y0 = 0
t0 = 0

# 0- R parameter
# 1- C parameter
# 2- Vin step
arg = [100, 0.01, 5]
arg2 = [200, 0.005, 5]

r = ode(f).set_integrator('vode')
r.set_initial_value(y0,t0)
r.set_f_params(arg)

r2 = ode(f).set_integrator('vode')
r2.set_initial_value(y0,t0)
r2.set_f_params(arg2)

t_final = 10
dt = 0.1

t = [t0]
v1 = [y0]
v2 = [y0]

while r.successful and r.t < t_final \
        and r2.successful and r2.t < t_final:
    
    r.integrate(r.t + dt)
    r2.integrate(r2.t + dt)

    #r2.integrate(r2.t + dt)
    #r.integrate(r.t + dt)
    
    print "1: ", r.t, r.y
    print "2: ", r2.t, r2.y
    
    t.append(r.t)
    v1.append(r.y)
    v2.append(r2.y)
    
## plot the simulation
from matplotlib import *
from pylab import *
figure(1)    #Using matplotlib
plot(t,v1,t,v2)
title('RC circuit')
xlabel('Time')
show()

----------------------------------------------------------------------

What could be the problem?

Also, I'm new to Python and I'm still trying to grasp how to best use
it.

Thanks in advance,
Vitor Matos