odeint for an differential system

Question

I have a problem with odeint. I have to solve an first order differential system and then a second order system but I am a little confused with the first order one. Can you explain what I have marked as wrong? Thank you :)

import scipy.integrate as integrate
import numpy as np
def fun(t,y):
  ys = np.array([y[1], (1-y[0]**2)*y[1]-y[0]])
  return(ys)
N = 3
x0 = np.array([2.00861986087484313650940188,0])
t0tf = [0, 17.0652165601579625588917206249]
T=([0 for i in range (N+1)])
T[0]= t0tf[0]
Pas = (t0tf[1]-t0tf[0])/N
for i in range (1,N+1):
       T[i]= t0tf[0] + i*Pas
X = integrate.odeint(fun, x0,T,Dfun=None, col_deriv=0,full_output=True)
T = np.array(T)
T = T.reshape(N+1,1)
S = np.append(X,T,axis=1)
print(S)

The returned error is:

ys = np.array([y[1], (1-y[0]**2)*y[1]-y[0]])

TypeError: 'float' object is not subscriptable

Answer 1

You need to reverse the order of the arguments to your derivative function - it should be f(y, t), not f(t, y). This is the opposite order to that used by the scipy.integrate.ode class.

Also, the concatenation S = np.append(X,T,axis=1) will fail because X is a tuple containing your integrals and a dict. Use S = np.append(X[0],T,axis=1) instead.