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Hello Paul,
You wrote:
>Um. CEERAN0 updates the seed, in order to _give_ you a pseudorandom
>sequence. If you reset the seed to zero each time, you are tinkering with
>the pseudorandom algorithm, and I would expect the results to be less
>"random" than using the returned seed value.
I know CEERAN0 updates the seed. That's why I suggested changing it on each
call. All
that does is start the sequence again and will quite likely result in numbers
that are
badly random, however Mike didn't seem to actually want random numbers, only
different
numbers. He is going to have to experiment to find a solution that fits his
requirements. Note the use of 'may' in my suggestion ... read Knuth's quote
again.
Another possibility is to generate a sequence of pseudo-random numbers from a
seed of
zero and once finished with that sequence reset the seed to zero and do it
again. Since
the GMT is likely to be different the sequence will be different (although the
same
numbers could be generated). Since I don't know exactly what GMT means when
used by the
API I could be completely wrong but I'd guess that it means the time_t returned
by the
time() function which is the number of seconds since EPOCH (00:00:00 Jan 1st,
1970 --
the supposed birth of Eunuchs). Since that value is constantly incrementing
the seed
will never be the same.
>Of course, I could be wrong (I believe this has happened at least twice :),
>but my experiments with CEERAN0 shows that it gives a nicely uniform
>frequency distribution.
It does, but Mikes 'problem' was avoiding repeating sequences due to using the
same
seed which can't be done without changing the seed.
Here is a trivial example program written in free-format RPG:
#include <stdlib.h>
#include <stdio.h>
#include <lemath.h>
int main(void)
{
int x=0,y=0;
double f=0.0;
printf("Random numbers with zero seed using CEERAN0\n");
for (x = 1; x <= 10; x++)
{
y=0;
printf("seed=%d, ", y);
CEERAN0( &y, &f, NULL);
printf("iteration %d, rand=%f, seed=%d\n", x, f, y);
}
}
The program generated the following output:
Random numbers with zero seed using CEERAN0
seed=0, iteration 1, rand=0.939558, seed=2017684432
seed=0, iteration 2, rand=0.267679, seed=574836272
seed=0, iteration 3, rand=0.153093, seed=328765360
seed=0, iteration 4, rand=0.923922, seed=1984107216
seed=0, iteration 5, rand=0.252043, seed=541259056
seed=0, iteration 6, rand=0.137458, seed=295188160
seed=0, iteration 7, rand=0.908286, seed=1950530016
seed=0, iteration 8, rand=0.236408, seed=507681840
seed=0, iteration 9, rand=0.564529, seed=1212317328
seed=0, iteration 10, rand=0.892651, seed=1916952816
Regards,
Simon Coulter.
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