RE: ceerano and the seed -- MIDRANGE-L

 I agree that it doesn't work well for what we were trying to do.  What made
me most curious was the pattern of the results.  A small subset of the
numbers each occurred 70 and 69 times each with the remainder each occurring
once over 99,999 iterations. I would have expected something more like a
normal distribution.

Since we were trying to put together numbers in a sequence that appeared
random, it would probably be easier to use FMTDTA to shuffle a preselected
range.

-----Original Message-----
From: Hans Boldt
To: midrange-l@midrange.com
Sent: 9/17/2002 5:31 AM
Subject: Re: ceerano and the seed

Joel Fritz wrote:
> We've been playing with CEERANO to try to construct a list of 13 digit
> unique numbers in "random" order.  It looks like that after 20,000 or
so,
> diminishing returns sets in in a big way.
>
> What we're doing is starting with zero as the seed and using whatever
gets
> returned in the seed parm as the next seed.  The test program looks at
its
> output file to see if the current random number is in the file.  If
not, it
> writes it.  Out of curiosity I tried a run of 99,999--off by 1
<g>--just to
> see what I'd get.  1322 of the numbers occurred 70 times, 29 of them
> occurred 69 times, and the others occurred once.  I guess I'd expect
the
> frequencies to be a little more normally distributed.
>
> Looks like using the seed value returned by the function is not a good
idea.
> Does anyone know what's happening here?

If you look at the documentation for ceeran0, you'll see that using
the seed value returned by the function for the next iteration is
exactly how the seed was intended to be used.  The documentations
states: "On return, CEERAN0 changes the value of seed so that it may
be used as the new seed in the next call."  That's the way many
pseudo-random number generators are supposed to work.

Using the current time is not a good choice for each iteration since
the time may not change between iterations, or may change in too
predictable a fashion.

Clearly, using random numbers is not the best technique to generate
"unique" numbers, and you should perhaps look at some better
technique.  One way to generate unique numbers is to start at 1, and
increment for each new number.  If you want the numbers to "look"
random, then start with some big number, say 293756927, keep
incrementing that, but return the number with the digits rearranged
in some sytematic manner.

Cheers!  Hans



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