[SciPy-User] Troubles with odeint or ode

ANDREA ARMAROLI rmrndr@unife...
Tue Nov 3 13:04:57 CST 2009

```Dear users,

I'm trying to solve an ODE system that models a parametric oscillator with
complex amplitudes at two freqencies.

I'm new to python. This problem is simply solved in matlab using ode45.

If I try to use odeint I cannot set parameters like tolerances or max step.

The result is constant-valued solutions.

Trying with ode class and ZVODE integrator, I have that total intensity is not
conserved. I have weird quasi-periodic oscillations.

I do know that my equations have excess degrees of freedom and I know from
symmetries what the integrals of motion are, but in Matlab this works pretty well.

Here is the code with odeint

import numpy as N
import scipy as S
import scipy.integrate
import pylab as P

def deriv(Y,t):

A1 = Y[0]
A2 = Y[1]
A1d = 1j*A2*N.conj(A1)
A2d = 1j*(A1**2/2.0 + dk*A2)
return [A1d, A2d]

nplot = 10000
zmax = 10.0
zstep = zmax/nplot

dk = 0.5 # normalised detuning/dispersion
phi0 = 0.0*N.pi # initial dephasing
eta0 = 0.3 # initial pump intensity

# initial values
u20 = N.sqrt(eta0)*N.exp(1j*phi0)
u10 = N.sqrt(2*(1-eta0))

H0=dk*eta0+2*N.sqrt(eta0)*(1-eta0)*N.cos(phi0);

Y,info =
scipy.integrate.odeint(deriv,[u10,u20],N.arange(0,zmax+zstep,zstep),full_output=True,printmessg
= True)
# are conserved quantities constant?
Ptot = N.abs(Y[:,0])**2/2+ N.abs(Y[:,1])**2
P.plot(N.arange(0,zmax+zstep-0.0001,zstep),Ptot)
# then Hamiltonian...
#...

p1  = P.plot(N.arange(0,zmax+zstep-0.0001,zstep),N.abs(Y[:,0]))
p2  = P.plot(N.arange(0,zmax+zstep-0.0001,zstep),N.abs(Y[:,1]))

Thank you very much for your help.

Andrea Armaroli

```