Re: Controlling ('rand') random number upper limit

Chris, Paul,

That being said, Paul's solution can still be screwed, depending
on how the system is adjusting for math.  One out of 32767 times
it will return a value 1 greater than his range.

For a range 1 to 10 (normal return):
32766 / 32767 = 0.999969481 * 10 = 9.99969481.  Truncate returns
9.  +1 = 10.  Top range.
But, that 32767'th time, 
32767 / 32767 = 1 * 10 = 10.  + 1 = 11.  Ooops.

The larger the range returned the less this will happen, but it is
still a possibility.  In my functions, I had always looked for this,
if RangeReturn = TopRange + 1, recursively call the subroutine.

Other options include just throwing that "extra" one into the toprange.
if RangeReturn = TopRange + 1, RangeReturn = TopRange.

With one returning a number from 0 to .9999999999 this isn't a problem.

Regards,

Jim Langston

Me transmitte sursum, Caledoni!

Chris Rehm wrote:
> 
> Paul Jackson wrote:
> 
> Paul, the solution you found is the most accurate one. You can, as been
> pointed out, simply divide the random number generated by the range of
> the number you want and take the remainder. But that is not exactly
> accurate. Let's suppose you wish to generate a number between 1 and
> 100.  327 times out of 328 it will return a number between 0 and 99, add
> one and you have the random number you wanted to generate. But once out
> of 328 tries it will generate a number between 32700 and 32768, not
> 32799. So there is no chance you will generate a number between 69-100
> using this method. So your random generation is slightly skewed.
> 
> The method you have found, using the ratio of the number to it's range
> and applying that to the range of number that you want will give as a
> distribution that is as random as the numbers provided by the generator.
> 
> All that said, it might be that the generator isn't all that flat
> either, and you might not care if you are all that perfect in your
> distribution (I don't know your application). So you just need to decide
> between accuracy and ease of coding.
+---
| This is the RPG/400 Mailing List!
| To submit a new message, send your mail to RPG400-L@midrange.com.
| To subscribe to this list send email to RPG400-L-SUB@midrange.com.
| To unsubscribe from this list send email to RPG400-L-UNSUB@midrange.com.
| Questions should be directed to the list owner/operator: david@midrange.com
+---