Re: CEERAN0 API

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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