Beowulf Questions

Bryce Bockman bockmabe at plu.edu
Tue Jan 14 22:23:24 EST 2003


Thanks for the info Robert.  This is good stuff.

Cheers,
Bryce

Robert G. Brown wrote:

>On Tue, 14 Jan 2003, Bryce Bockman wrote:
>
>  
>
>> From a theoretical standpoint I can't add too much to this debate, but
>>when I was writing an extension to Mathew Walls GALib (a genetic
>>algorithms library) I used MPI to implement a collection of "Island
>>Model" genetic algorithms.  Initially, I took no steps to make sure that
>>the random number pools didn't overlap other than using different seeds
>>(node id along with time) on each node.  Mathew's library implements the
>>famous ran2 from numerical recipes.  However, when I finally did
>>implement a leapfrog method for guaranteeing disjoint sets, my solutions
>>began to converge much more quickly.  So my guess is that making sure
>>that I had unique pools did help in my case.  Clearly GAs are one of the
>>more RNG intensive applications, but I think there is a case for using a
>>leapfrog method on small clusters or if your random number generator
>>permits it, a look ahead technique that allows you to partition your
>>pseudo random number space on a per node basis.  Or use of the SPRNG
>>library which was mentioned earlier.
>>    
>>
>
>Anyone preparing to use RNG's seriously should (these days) likely START
>with the latest version of the Gnu Scientific Library (gsl), which is
>getting quite sophisticated and complete time passes and lots of very
>talented people continue to contribute.
>
>I'm playing with a fairly recent but not even bleeding-edge current
>snapshot of the library, and there are (or were recently) 56 different
>RNG's encapsulated in the library's one basic call wrapper, selectable
>either in code or via an external environment variable.  The best of
>these is very good indeed -- it passes the DIEHARD tests, has a period
>of something truly absurd like 10^6000, and is almost as fast as NR's
>ran3 (which fails DIEHARD and has an uncomfortably short period).  With
>a period like this, getting non-overlapping seeds from e.g. /dev/random
>is likely enough for "any" application (in quotes so that I can better
>withstand it when somebody tells me why this is wrong and I'm silly to
>even think it for THEIR application...:-)
>
>I'm embedding the gsl in a testing/benchmarking wrapper designed to JUST
>test (against e.g.  diehard and sts/fips), benchmark, and demonstrate
>all these RNG's in a shell that makes it fairly easy to test standalone
>generators or hardware generators or new subroutine-level generators.
>This is a natural extension of my benchmarking /dev/random for speed
>last week.  I'll probably announce it on the list if/when I ever finish
>it.
>
>The GSL manual (http://sources.redhat.com/gsl/ref/gsl-ref_toc.html) is
>an excellent numerical resource to benchmark.  It is a good idea to read
>its discussion of RNG's, look over the generators it provides (including
>many old/obsolete/known bad generators for comparison purposes).  It is
>a generally BAD idea to use ANY code from Numerical Recipes.  There is a
>lovely online rant against NR that scathingly picks it apart in terms of
>the quality of its algorithms.  It also has a horribly restrictive
>copyright and license, if one actually takes the time to read it.
>Currently, one can't even use NR in one's own code on one's own machine
>unless one owns the book and types in the code BY HAND.  Licenses for
>machine readable access for multiple machines, networks, multiple users,
>and so forth are ruinously expensive.
>
>Before the GSL matured, NR might have been one of the few games in town
>along with even more expensive IMSL, NAG and so forth.  At this point,
>the GSL is powerful, extensive, portable, GPL, extensible, etc, etc.  So
>far, I've found its routines to be of high quality with a few exceptions
>where the code "just wasn't finished" yet.  There are a lot of very good
>numerical coders contributing now, and many areas are very well covered
>indeed (the table of contents alone is nearly 1000 lines long).
>
>   rgb
>
>Robert G. Brown
>http://www.phy.duke.edu/~rgb/ 
>Duke University Dept. of Physics, Box 90305 Durham, N.C. 27708-0305 
>Phone: 1-919-660-2567 Fax: 919-660-2525 email:rgb at phy.duke.edu
>
>
>  
>


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