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Re: Optimization Question: Sum at each element of array [message #75100 is a reply to message #75083]

Tue, 15 February 2011 06:31

Jeremy Bailin
Messages: 618
Registered: April 2008

Senior Member

On Tuesday, February 15, 2011 12:58:02 AM UTC-5, Charles Steinhardt wrote:
> Hello,
>
> I'm trying to optimize the following:
>
> for i=0, 100 do begin
> y = y + myfunc(x, x + sigma * (i-50)/10.0, P[2]*myfunc2(x + sigma
> * (i-50)/10.0), sigma)
> endfor
>
> Here, x, y, and sigma are arrays of the same cardinality. I know the
> for loop is slow in IDL compared to array operations, but I'm having
> problems finding a faster way to do this. Is it really faster to make
> an array of findgen(101) and then do some sort of summation over
> that?
>
> I'm hoping somebody has run into this before - I'd appreciate any
> advice you have!
>
> Thank you,
>
> -Charles

It depends on myfunc and myfunc2. It looks like myfunc currently takes 3 arguments of the same cardinality, and myfunc2 takes one argument? If they can be written in such a way that they can take an extra dimension (of length 101, in this case), then yes, it would be faster to just do a total. So, for example:

xsize = size(x, /dimen)
ndimen = n_elements(xsize)
fullsize = [xsize,101]
xfull = rebin(x, fullsize, /sample)
sigmafull = rebin(sigma, fullsize, /sample)
ifull = rebin( (findgen(101)-50)/10., fullsize, /sample)

y = total( myfunc(xfull, xfull + sigmafull * ifull, $
P[2]*myfunc2(xfull + sigmafull * ifull), sigmafull), ndimen )

-Jeremy.

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[Message index]

		Re: Optimization Question: Sum at each element of array By: James[2] on Tue, 15 February 2011 12:15
		Re: Optimization Question: Sum at each element of array By: Jeremy Bailin on Tue, 15 February 2011 06:31
		Re: Optimization Question: Sum at each element of array By: Brian Daniel on Tue, 15 February 2011 05:09

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