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Re: Randomu seed initialization [message #68610 is a reply to message #68609]

Thu, 12 November 2009 13:49

Chris[6]
Messages: 84
Registered: July 2008

Member

On Nov 12, 10:32 am, sav...@nsidc.org wrote:
> Jeremy Bailin <astroco...@gmail.com> writes:
>> If I had to speculate, I'd say that the variable that you're passing
>> as the seed isn't undefined like you think it is. Have you tried doing
>> a "help, seed" right before the randomu call?
>
> If I was going to speculate, I would guess the undefined seed gets set
> to the same value internally every time. Thereby starting the same
> string of pseudo-random numbers.
>
> I usually use:
> seed = long(systime(/seconds) )
>
> To initialize my seed. It's not perfect, but it's a start.
>
> Also remember from the docs: "Each independent random number sequence
> should maintain its own state variable. To maintain a state over
> repeated calls to a procedure, the seed variable may be stored in a
> COMMON block."
>
> Matt
>
> --
> Matthew Savoie - Scientific Programmer
> National Snow and Ice Data Center
> (303) 735-0785 http://nsidc.org

I've hit this issue before - calling RANDOMU with an undefined seed
many times produces collections of random numbers with very similar
properties. It's weird.

Successive calls to randomu which save the seed value avoid this
problem. Whenever I use randomu in a function, I do something like

function junk
common junk_seed, seed
x = randomu(seed)
return, x
end

which keeps track of the seed value automatically.

chris

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[Message index]

		Re: Randomu seed initialization By: Conor on Fri, 13 November 2009 08:31
		Re: Randomu seed initialization By: pgrigis on Thu, 12 November 2009 13:59
		Re: Randomu seed initialization By: Chris[6] on Thu, 12 November 2009 13:49
		Re: Randomu seed initialization By: Matt[2] on Thu, 12 November 2009 12:32
		Re: Randomu seed initialization By: Jeremy Bailin on Thu, 12 November 2009 11:31
		Re: Randomu seed initialization By: Conor on Thu, 12 November 2009 05:59
		Re: Randomu seed initialization By: penteado on Wed, 11 November 2009 12:22

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