Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!apple!tahoe!jimi!arrakis!ramesh
From: ramesh@nevada.edu (RAMESH VISWANATHAN)
Newsgroups: comp.lang.idl-pvwave
Subject: Re: How can I integrate? (easy question?)
Message-ID: <1991Mar25.173317.15255@nevada.edu>
Date: 25 Mar 91 17:33:17 GMT
References: <1991Mar20.233728.1@csc.anu.edu.au>
Organization: University of Nevada, System Computing Services
Lines: 22

In article <1991Mar20.233728.1@csc.anu.edu.au> bdb112@csc.anu.edu.au writes:
>How can I efficiently do a running sum of a vector (integrate)?  The explicitly
>coded version (IDL v2)  
>for i=1,n-1  x(i)=x(i) + x(i-1) achieves the desired effect, but takes (VS3100)
>1 second for a 2000 element array compared to .01 sec for z=x+x, a similar
>number of operations.  This is such an obvious thing to do that I must be
>missing something obvious - I can't find it in the userlib either (just
>deriv).


Assuming "i" represents the current array index value upto which you want to
sum the elements of the array "x", try:

	sum_x = total(x(0:i))

or a variation thereof.  The dimension of array "sum_x" will be automatically
dimensioned to the value contained in "i"

Note: Function "total" is a PV Wave system routine.


R.V.