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FOR loops and efficiency [message #66568]

Thu, 21 May 2009 09:04

Rachel
Messages: 6
Registered: June 2000

Junior Member

It was impressed upon me sometime or another that the use of FOR loops
in IDL applications tends to be an inefficient solution for doing many
tasks, yet sometimes I have difficulty finding a reasonable
alternative to the FOR loop. I was wondering if anyone could give me
advice on the following example code.

I am trying to make a function that takes arrays of parameters and
then generates a mathematical model. In the following example I use
gaussian curves, but generally I would want to expand an
implementation to other mathematical functions (gaussians are just
easy for this example).
So basically I can accomplish what I want to do using something like
the following:

x = findgen(2000)*0.1 + 900.0
y = fltarr(2000)+1.0

lam0 = findgen(10)*50.0 + 900.0
depth = findgen(10)/10.0
width = findgen(10)

for i = 0,n_elements(lam0)-1 do y = y *(1.0 - depth[i]*exp(-(x-width
[i])^2/2.0/width[i]))

I was thinking about how one might accomplish the same things without
a for loop and I came up with the following... problem being that for
large arrays of lam0 this is actually more inefficient (I'm assuming
because of the use of extraordinarily large arrays)

n = n_elements(x)
nlines = n_elements(lam0)
y = product(1.0 - rebin(transpose(depth),n,nlines)*exp(-(rebin
(x,n,nlines)-rebin(transpose(lam0),n,nlines))^2/2.0/rebin(tr anspose
(width),n,nlines)),2)

any advise?

Thanks!
Josh

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[Message index]

		FOR loops and efficiency By: Rachel on Thu, 21 May 2009 09:04
		Re: FOR loops and efficiency By: JDS on Tue, 26 May 2009 14:51
		Re: FOR loops and efficiency By: Craig Markwardt on Wed, 27 May 2009 22:38
		Re: FOR loops and efficiency By: Craig Markwardt on Sat, 23 May 2009 13:24
		Re: FOR loops and efficiency By: JDS on Fri, 29 May 2009 13:39
		Re: For loop By: Hassan on Tue, 27 October 2009 01:16
		Re: For loop By: Michael Galloy on Mon, 26 October 2009 09:47
		Re: For loop By: Hassan on Mon, 26 October 2009 08:45
		Re: For loop By: penteado on Mon, 26 October 2009 08:01

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