Shaun - 6 months ago 63

Python Question

Hi I have the following function which produces an out of bounds error:

`import numpy as np`

import pylab as plt

import scipy

import math

import sympy as sy

T = sy.Symbol('T')

rho = sy.Symbol('rho')

g_T = [1,T,T**2,T*sy.log(T),T**2*sy.log(T)]

g_rho = [1,rho,rho**2,rho*sy.log(rho),rho**2*sy.log(rho)]

g_T_np = np.asarray(g_T)

g_rho_np = np.asarray(g_rho)

c = np.loadtxt("c_test.txt")

def F(T,rho):

ret = 0

for n in xrange(1,5):

for m in xrange(1,6):

inner= c[n,m]*g_T_np*g_rho_np

ret += inner

return ret

print F(T,rho)

where the .txt file is like this:

`-0.529586 -0.000208559 -3.36563E-09 2.29441E-05`

2.22722E-06 -0.00014526 -2.48888E-09 1.89488E-05

-6.26662E-05 0.000421028 6.17407E-09 -5.14488E-05

0.09977346 -0.000622051 -8.56485E-09 7.49956E-05

-0.01437627 -9.86754E-05 -1.59808E-09 1.22574E-05

The full error displayed is:

`Traceback (most recent call last):File "EOS_test.py", line 38, in <module> print F(T,rho) File "EOS_test.py", line 31, in F inner=c[n,m]*g_T_np*g_rho_np IndexError: index 4 is out of bounds for axis 1 with size 4`

How can I solve this error?

Answer

Numpy uses 0-based indexing. From the looks of it you are indexing the array from 1 (2nd position) to 4 (5th position), which is of course out of bounds for the array you are working with. The same is true for the second axis.

Secondly, you've mixed up your axes:

- The first axis (0) is the index of the selected row (0 to 5)
- the second axis indexes the column, i.e. the value inside a row (indexed 0 to 4)

This should work:

```
def F(T,rho):
ret = 0
for n in range(5):
for m in range(4):
inner= c[n,m]*g_T_np*g_rho_np
ret += inner
return ret
```