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Re: x*x versus x^2 [message #61201 is a reply to message #61200]

Wed, 09 July 2008 09:55

pgrigis
Messages: 436
Registered: September 2007

Senior Member

Probably this happens because you raise to a floating point
exponent, and likely IDL computes an exponential function,
which is slower.
If you try x^2 (not x^2.0) it is possible that the compiler
optimizes it to x*x.

Ciao,
Paolo

Conor wrote:
> So I've been looking at execution time for various algorithms, and I
> found this interesting result:
>
> bigarr = fltarr(1000,1000)
>
> t1 = systime(/seconds)
> t = bigarr^2.0
> t2 = systime(/seconds)
> t = bigarr*bigarr
> t3 = systime(/seconds)
>
> print,t2-t1
> print,t3-t2
>
>
> IDL prints:
>
> 0.024163008
> 0.010262012
>
> Apparently multiplying an array by itself is twice as fast as using
> the carat operator! Anyone know why this is? Is it a memory issue or
> something?

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[Message index]

		Re: x*x versus x^2 By: Conor on Wed, 09 July 2008 10:10
		Re: x*x versus x^2 By: Bruce Bowler on Wed, 09 July 2008 09:57
		Re: x*x versus x^2 By: pgrigis on Wed, 09 July 2008 09:55
		Re: x*x versus x^2 By: Conor on Wed, 09 July 2008 09:43
		Re: x*x versus x^2 By: dzhang49 on Sat, 12 July 2008 09:25

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