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Re: [Bug-gsl] initialisation of random number generator on 64bit machine

From: Brian Gough
Subject: Re: [Bug-gsl] initialisation of random number generator on 64bit machine
Date: Mon, 15 Sep 2008 15:57:30 +0100
User-agent: Wanderlust/2.14.0 (Africa) Emacs/22.2 Mule/5.0 (SAKAKI)

At Fri, 12 Sep 2008 16:52:48 +0200,
Vito Trianni wrote:
> Please find attached an example program that reproduces the error I  
> was experiencing. I tested it on both 32- and 64-bit architectures,  
> and it actually does not produce random values on the latter (see the  
> "local" values in the last line of output: it varies across different  
> runs on 32-bit architectures, but it does not on 64-bit ones).

Thanks for the example program.

What is happening here is that your seeding expression
floor(value*((1.0 + max - min)+min)) always returns values which are
multiples of 2^32, due to the limited range of double values being
returned. These are mapped to the same seed (zero) modulo 2^32.

I have added a note to the manual that the generators only accept
32-bit seeds.

Brian Gough

GNU Scientific Library -

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