Re: random

[Benedikt Stefansson]

Amber L. Hinkle wrote:

> I am trying to generate random numbers with an exponential distribution.
> First, I don't know what generator to use.  I also can't seem to be able
> to use command line parameters with the Cygnus Cygwin32 bash shell.  I
> think using the command -varySeed would help but I can't get it to work.

Hi,

When you execute the function swarmInit() the Swarm kernel sets up a default
random number generator. This is, according to Sven's documentation, a
Mersenne Twister type generator with a single cycle of length 2^19937-1
which I think is the longest reported in the literature, in other words
pretty darn good. If you buy that, and since the pointer to the default
random number generator, "randomGenerator" is a global variable, you can
simply create and initialize your exponential distribution object thusly:

exponentialDistribution=[ExponentialDist create: [self getZone]
setGenerator:  randomGenerator setMean: mean];

Where mean is a parameter which you choose. Since you are most probably
creating the generator in a Swarm, you can also substitute "self" for "[self
getZone]".

If you want to control the random number seed, insert this line before you
call the exponential distribution for the first time:

[randomGenerator setStateFromSeed: randomSeed];

where randomSeed is a parameter which you choose. This primes the generator,
and since you can control the parameter it's much better than using
--varySeed.

For more info refer to:

http://www.santafe.edu/projects/swarm/swarmdocs/html/set/swarm.random.sgml.reference.html

Regards,
-Benedikt
----------------
Benedikt Stefansson                 address@hidden
Department of Economics, UCLA       Fax. (310) 825-9528
Los Angeles, CA 90095-1477          Tel. (310) 825-1777


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