WARNING on Numerical Recipes in C

[donalson]

I have come upon two instances where there were major errors caused by using
Numerical Recipies.  The first occurance was when a post-doc in mathmatical
ecology
was getting strange results from from the same simulation but using different
loop structures.
After a fair amount of discussion I suggested that he try another generator,
even something
as simple as RAND() to see what happened.  Because the generator he was using
was from
such a respected source, he was very resistent but eventually agreed to try
it.  The
problem went away.

Last month an almost idential situation happened, this time with a
physics/mathmatical ecology
doctoral student.  Given that there was no apparent reason for the simualtion
behavior, I suggested
she try, (for test purposes only) RAND().  One again, the anomalies
disappeared.

There are obviously potentially serious problems with some of the RNG
algorithms in
Numerical Recipies, I don't know where they stem from nor which generators
were
involved.  I do know that both individuals involved are very competent
programmers
and mathematicians, so the likelyhood of programming error on their part is
very low.

Moral of the story, run a good set of tests (Swen has provided references for
a bunch
of them in the swarm docs) before you depend on a generator from this
reference.

D3

--
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* Doug Donalson                 Office: (805) 893-2962
* Ecology, Evolution,           Home:   (805) 961-4447
* and Marine Biology            email address@hidden
* UC Santa Barbara
* Santa Barbara Ca. 93106
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*
*   The most exciting phrase to hear in science, the one that
*   heralds new discoveries, is not "EUREKA" (I have found it) but
*   "That's funny ...?"
*
*       Isaac Asimov
*
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