Question

I want to do a double integral in python. Taking help from http://docs.scipy.org/doc/scipy/reference/tutorial/integrate.html, I did the following

import numpy as np
import matplotlib.pyplot as plt
from scipy import integrate


def func(x,a):
    return a*x*x

def integrl(a):
    return integrate.quad(func,0,10,args=(a))

print integrate.quad(lambda x: integrl(x),0,1)

But I get the following error

Traceback (most recent call last):
File "test.py", line 12, in <module>
print integrate.quad(lambda x: integrl(x),0,1)
File "/usr/lib/python2.7/dist-packages/scipy/integrate/quadpack.py", line 245, in quad
retval = _quad(func,a,b,args,full_output,epsabs,epsrel,limit,points)
File "/usr/lib/python2.7/dist-packages/scipy/integrate/quadpack.py", line 309, in _quad
return _quadpack._qagse(func,a,b,args,full_output,epsabs,epsrel,limit)
quadpack.error: Supplied function does not return a valid float.

What should I do?

Answer 1

The mistake is in the integrl function. In that I should specify which argument to integrate with. The correct code should read

import numpy as np
import matplotlib.pyplot as plt
from scipy import integrate


def func(x,a):
   return a*x*x

def integrl(a):
   return integrate.quad(func,0,10,args=(a))[0]

print integrate.quad(lambda x: integrl(x),0,1)