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Re: Random Sampling Without Replacement [message #72947 is a reply to message #72875]

Thu, 14 October 2010 05:27

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Heinz Stege writes:

> Okay, I see. What I wanted to say is, that one has to take care of the
> seed. And it is my preference, to put it into the parameter list.
>
> I am afraid, that I would forget about the today's common block, and
> generate a second one within another routine in half a year. :-)

Yes, half a year later you would probably be fine. However,
if you were doing this in some like of loop, maybe using
a bootstrap process or something, passing in the seed
as a parameter is often problematic. To get a truly
random sequence of numbers, the seed has remain "alive"
between calls to RandomU. Otherwise, you get the same
"random" sequence of numbers coming out of your program.

I think a lot of people don't realize this.

Cheers,

David

--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Sepore ma de ni thui. ("Perhaps thou speakest truth.")

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[Message index]

		Random Sampling Without Replacement By: David Fanning on Wed, 13 October 2010 08:46
		Re: Random Sampling Without Replacement By: David Fanning on Thu, 14 October 2010 05:27
		Re: Random Sampling Without Replacement By: Heinz Stege on Thu, 14 October 2010 03:44
		Re: Random Sampling Without Replacement By: David Fanning on Wed, 13 October 2010 20:19
		Re: Random Sampling Without Replacement By: Heinz Stege on Wed, 13 October 2010 19:59
		Re: Random Sampling Without Replacement By: Heinz Stege on Wed, 13 October 2010 18:14

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