Python/numpy Index Error

Question

I have the following modified section of code, which is mimicking a section of MatLab code, which works fine;

import numpy as np
import math

dt = 1e-2;                      # time step
t = np.arange(0, 7, dt)         # t

mt=2
nt=2

rho=np.zeros((2,2,2,2))

Pe=np.array([[1,0],[0,0]])
Sm=np.array([[0,0],[1,0]])
Sz=np.array([[1,0],[0,- 1]])
Sy=np.array([[0,- 1j],[1j,0]])
Sx=[[0,1],[1,0]]

exp_Sz=np.zeros((2,2,len(t)))
exp_Sy=np.copy(exp_Sz)
exp_Sx=np.copy(exp_Sz)
exp_Pe=np.copy(exp_Sz)


for indx in (1,mt):
    for jndx in (1,nt):
        exp_Sz[indx,jndx,1]=np.trace(rho[:,:,indx,jndx] * Sz)
        exp_Sy[indx,jndx,1]=np.trace(rho[:,:,indx,jndx] * Sy)
        exp_Sx[indx,jndx,1]=np.trace(rho[:,:,indx,jndx] * Sx)
        exp_Pe[indx,jndx,1]=np.trace(rho[:,:,indx,jndx] * Pe)

But I get the following error;

exp_Sz[indx,jndx,1]=np.trace(rho[:,:,indx,jndx] * Sz)
IndexError: index 2 is out of bounds for axis 3 with size 2

I am unsure on what the error is.

Any help would be appreciated, Thanks!

I recommend you read this guide for MATLAB users before asking any more questions: wiki.scipy.org/NumPy_for_Matlab_Users — rayryeng
– rayryeng, Commented Mar 14, 2015 at 5:05

wim · Accepted Answer · 2015-03-14 04:34:16Z

1

for indx in (1,mt):
    for jndx in (1,nt):
         # etc

The nested loops above iterate over the two element tuples containing only the elements 1 and mt (outer loop) and 1 and nt (inner loop).

You probably wanted to iterate over range(mt) and range(nt) instead.

Note that numpy arrays are 0-index based.

answered Mar 14, 2015 at 4:34

wim

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