my loop is too slow

[Tim Hochberg]

SC Zhong wrote in message ...
>
>I tried to learn and use python a week ago, and wrote
>a small application.  When it run the loop:
>
> for k in range(dimension):
> for i in range(dimension):
> for j in range(dimension):
> for h in range(dimension):
> a[k,i]=a[k,i]+c[k,h]*c[k,j]*\
> f[j,i]*f[i,h]


Are you using Numeric Python? The array notation ([x,y]) would indicate that
you are either using Numeric or your are using dictionaries to represent
arrays. If you are doing the second, it is likely to be quite slow.

If you are using or can use Numeric, something like the following (untested)
code should speed things up significantly.

from Numeric import *
dimRange = range(dimension)
# Make sure a is an array.
a = asarray(a)
for j in dimRange:
    for h in dimRange:
        a = a + (c[:,h]*c[:,j])[:,NewAxis] * (f[j,:]*f[:,h])[NewAxis,:]