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Re: randomn problem [message #52951 is a reply to message #52949]

Mon, 12 March 2007 02:07

Paolo Grigis
Messages: 171
Registered: December 2003

Senior Member

The problem does not lie with randomn, but with
stddev. If you compute it using double precision
instead, the problem should solve itsef. Example:

a=fltarr(3e7)
a[0:3e7/2]=1.

print,stddev(a)
0.528791
print,stddev(a,/double)
0.50000000

Ciao,
Paolo

askemer@gmail.com wrote:
> Hi all,
>
> I was playing around with randomn and noticed some weird behavior:
>
> IDL> print, stddev(randomn(seed, 1e7))
>
> I consistently get back numbers around ~0.992. I've tried it on a
> different computer, and the result was not exactly the same, but
> similar. If I change 1e7 to 1e8, the problem gets worse, and I get
> ~0.853. I've tried the syntax with floats, integers, and longs, and I
> still get the same answer. Does anyone know what could be going on?
>
> -Andy
>

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[Message index]

		Re: randomn problem By: Ben Panter on Mon, 12 March 2007 09:17
		Re: randomn problem By: Nigel Wade on Mon, 12 March 2007 09:07
		Re: randomn problem By: Paolo Grigis on Mon, 12 March 2007 02:07
		Re: randomn problem By: Ingo von Borstel on Mon, 12 March 2007 01:03
		Re: randomn problem By: David Fanning on Sun, 11 March 2007 18:10
		Re: randomn problem By: askemer on Sun, 11 March 2007 16:04
		Re: randomn problem By: David Fanning on Sun, 11 March 2007 12:41
		Re: randomn problem By: JD Smith on Tue, 13 March 2007 09:25
		Re: randomn problem By: Paolo Grigis on Tue, 13 March 2007 04:03

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