calculating on matrix indices

[Brian Blais]

Hello,

In my attempt to learn python, migrating from matlab, I have the following problem. 
Here is what I want to do, (with the wrong syntax):

from numpy import *

t=arange(0,20,.1)
x=zeros(len(t),'f')

idx=(t>5)
tau=5
x[idx]=exp(-t[idx]/tau)  # <---this line is wrong (gives a TypeError)

#------------------

what is the best way to replace the wrong line with something that works: replace all 
of the values of x at the indices idx with exp(-t/tau) for values of t at indices idx?

I do this all the time in matlab scripts, but I don't know that the pythonic 
preferred method is.



			thanks,

				bb


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             bblais at bryant.edu
             http://web.bryant.edu/~bblais