[MITgcm-devel] portable random number generator

[Ed Hill]

On Sun, 2004-07-18 at 16:48, Andrea Molod wrote:
> hi all,
> 
> i would like to make a (slight) change in the portable number generator,
> port_rand, that is in model/src. i would like to add an argument to the
> call which would set the seed for the random number generator (at the
> start of each run). without this, reproducibility of the random numbers
> between runs with pickups at different times is not possible. 
> 
> i see that port_rand is used in the flt package and appears in ini_theta 
> for the held-suarez verification experiments, but is not active. so i will
> change the code in both of those places to add an argument to the port_rand 
> call, and will change port_rand to assign the seed from the dummy argument.
> 
> NOTE: the change to the flt package code will duplicate the current behavior 
> and re-set the seed to the same value it has now for the start of each run.
> to make a run reproducible with flt the choice of seed in that code should
> be revisited (ie, set it from myiter, or something like that).
> 
> any objections/comments? speak up soon!


Hi Andrea,

Would it make sense to add full check-pointing so that both the
"identical initial conditions" and the "pickup" cases can be handled
gracefully?  And perhaps we could make it a new package named "random"? 
Of course, by making these suggestions I'm also volunteering to help
write it.  :-)

One of the best (fast, well-documented, etc.) publicly available
pseudo-random-number generators (the "Mersenne Twister") has Fortran
versions:

http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/VERSIONS/FORTRAN/fortran.html
http://www.math.sci.hiroshima-u.ac.jp/%7Em-mat/MT/emt.html

and one of those implementations has the ability to save and re-load the
state of the generator for check-pointing and restarts.  So it can be
done and it doesn't look too difficult.

Ed

-- 
Edward H. Hill III, PhD
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