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Re: How can I integrate? (not so easy?) [message #146 is a reply to message #2]

Mon, 25 March 1991 12:18

bdb112
Messages: 3
Registered: March 1991

Junior Member

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).

Two respondents have suggested
sum_x = total(x(0:i)) ; where i is the maximum idex of the array
When I try this, I get a scalar result, rather like a definite integral, when
what I want is a vector which is a running total, like an indefinite integral.

e.g. x = [1,1,2] sum_x = [1,2,4]
Of course, the next step would be to allow an optional vector which contained
the abscissae, if not equally spaced, or the spacing if equally spaced, but I
would be happy with the simple result.

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[Message index]

		How can I integrate? (easy question?) By: bdb112 on Wed, 20 March 1991 04:37
		Re: How can I integrate? (not so easy?) By: bdb112 on Mon, 25 March 1991 12:18
		Re: How can I integrate? (easy question?) By: ramesh on Mon, 25 March 1991 09:33
		Re: How can I integrate? (easy question?) By: bruce on Thu, 21 March 1991 16:22

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