# CAMB python convergence power spectrum code

• sunrah

#### sunrah

I'm trying to understand this python CAMB code: http://camb.readthedocs.io/en/latest/CAMBdemo.html
Scroll down to In[29] and In[30] to see it.

It's an integration over chi (comoving distance), yet scipy.integrate.quad is not called. It seems that the fun stuff happens in the last for-loop in In[30], where they use numpy.dot to take dot product of two arrays. What's going on here? The first array is Delta-Chi (see In[29]) and the second is simply the integrand. So how is this integration? Thanks

I'v been messing around with this and found something interesting:

Python:
from __future__ import division
import numpy as np
import matplotlib.pyplot as plt

xmax = 10
N = 1000
xx = np.linspace(0,xmax,N)

dx = (xx[2:] - xx[:-2])/2
xx = xx[1:-1]
Nx = len(xx)
yy1 = np.arange(0,Nx, dtype=np.float64)
yy2 = []

f = lambda z: z**3

for ix, x in enumerate(xx):
foo = np.linspace(min(xx),x,N-2)**3
yy1[ix] = np.dot(dx, foo)
plt.plot(xx,yy2,label='quad')