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Re: Fast matrix filling in IDL [message #13791 is a reply to message #13788]

Fri, 11 December 1998 00:00

davidf
Messages: 2866
Registered: September 1996

Senior Member

Timm Weitkamp (weitkamp@my-dejanews.com) writes:

> What is the fastest way of filling a matrix with identical
> column vectors in IDL?
>
> More precisely, if A is a float matrix (m x n) and V is
> a vector with m elements, is there a faster way than
>
> FOR i=0,n-1 DO A[*,i]=V ?

I don't know about "fastest", but

vector = Replicate(1, n)
array = V ## vector

is about 5 times faster for a 1000 by 500 array.
Here is my example program:

************************************************************ *
PRO TEST

array = Fltarr(1000, 500)
v = RandomU(seed, 1000)

time = systime(1)
FOR i=0,500-1 DO array[*,i] = v
Print, 'Time for Loop: ', systime(1) - time

time = systime(1)
vector = Replicate(1, 500)
array = v ## vector
Print, 'Time for Matrix Operations: ', systime(1) - time
END
************************************************************ *

And the results:

IDL> test
Time for Loop: 0.10000002
Time for Matrix Operations: 0.019999981

Cheers,

David

--
David Fanning, Ph.D.
Fanning Software Consulting
Phone: 970-221-0438 E-Mail: davidf@dfanning.com
Coyote's Guide to IDL Progamming: http://www.dfanning.com/
Toll-Free IDL Book Orders: 1-888-461-0155

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[Message index]

		Re: Fast matrix filling in IDL By: Kevin Ivory on Mon, 14 December 1998 00:00
		Re: Fast matrix filling in IDL By: steinhh on Mon, 14 December 1998 00:00
		Re: Fast matrix filling in IDL By: davidf on Mon, 14 December 1998 00:00
		Re: Fast matrix filling in IDL By: Kevin Ivory on Mon, 14 December 1998 00:00
		Re: Fast matrix filling in IDL By: Phillip & Suzanne on Sat, 12 December 1998 00:00
		Re: Fast matrix filling in IDL By: davidf on Sat, 12 December 1998 00:00
		Re: Fast matrix filling in IDL By: steinhh on Sat, 12 December 1998 00:00
		Re: Fast matrix filling in IDL By: davidf on Fri, 11 December 1998 00:00

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