“'float' is not subscriptable” in odeint

Question

I'm trying to implement coupled differential equations in Python, and as a new user I seem to be stuck at something. I used this tutorial as a guide to how to solve my ODEs, and looked into the documentation to no available

This is where I define the function

def Burnout(t, y, m, nu, S0, V, delta, mu):
    S = y[0];

    E = [0 for i in range(0,m)]
    dEdt = [0 for i in range(0,m)]

    for i in range(0,m):
        E.append(y[i+1])

    P = y[m+1]

    dSdt = -nu*S*P*(S/S0)**V
    dEdt.append(nu*S*P*(S/S0)**V-m*delta*E[0])

    for i in range(1,m):
        dEdt.append(m*delta*E[i-1]-m*delta*E[i])

    dPdt = m*delta*E[m-1]-mu*P

    return [dSdt, *dEdt[0:m], dPdt]

Then, as in the tutorial, I define the initial conditions by

 S0 = N
 y0.append(S0)

 for i in range (0, m):
    E.append(0)
    y0.append(E[i])

 P0 = Z
 y0.append(P0)

where N and Z are previously defined things, and E was an empty array. When I finally call odeint(Burnout, y0, t, args = p), I get a 'float' object is not subscriptable pointing to my definition of S in my Burnout function. As I passed a list to odeint I'm kind of confused on why Python says I passed a float. Does anyone see what I did wrong? Thanks in advance!

EDIT: Ok, now here is a minimal, complete and verifiable example that gives me the same error

import numpy as np from scipy.integrate import odeint

 def Burnout(t, y, m, nu, S0, V, delta, mu):

    S = y[0]

    E = [0 for i in range(0,m)]
    dEdt = [0 for i in range(0,m)]

    for i in range(0,m):
        E.append(y[i+1])

    P = y[m+1]

    dSdt = -nu*S*P*(S/S0)**V
    dEdt.append(nu*S*P*(S/S0)**V-m*delta*E[0])

    for i in range(1,m):
        dEdt.append(m*delta*E[i-1]-m*delta*E[i])

    dPdt = m*delta*E[m-1]-mu*P

    return [dSdt, *dEdt[0:m], dPdt]


V = 2.97
m = 26
delta = 1/6
mu = 1
nu = 10
S0 = 5

t = np.linspace(0,56,100)

y = [10,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,100]
p = (m, nu, V, S0, delta, mu)
print(odeint(Burnout,y,t,args=p))

Answer 1

You ordered the arguments in your ode definition wrong. It is possible to have t before y , but then you must define tfirst = True (see docs) .

Swapping the arguments in your definition of Burnout fixes the problem for me.

def Burnout(y, t, m, nu, S0, V, delta, mu):
   # ...
   # rest of function
   # ...

Alternately you can define the additional keyword tfirst in the odeint call:

odeint(Burnout, y, t, args=p, tfirst=True)