Random algorithm

[Richard Gaskin]

Dave Cragg wrote:

> On 13 Nov 2008, at 19:38, Richard Gaskin wrote:
> 
>> Fortunately, it doesn't.  Rev sets the randomSeed to some non-fixed  
>> number (a truncated portion of the milliseconds?) each time it starts.
>>
>> This implies that each session starts with a unique seed, so each  
>> sequence derived from it will be similarly unique.
> 
> This occurred to me last night while reviewing my comment on your  
> seeding method. Does a different randomSeed guarantee a different  
> random sequence in the same way that the same seed produces the same  
> sequence?

"Guarantee" is a tough claim to verify, since it's possible that even a 
truly random sequence might by chance appear as a repeated pattern. :)

But to test this I made a simple test stack with a button and two 
fields, with this in the button script:

on mouseUp
   put empty into fld 1
   put empty into fld 2
   --
   -- Test 1: psuedo-random randomSeed:
   repeat 2
     set the randomseed to random(444444)
     repeat 10
       set the randomSeed to random(444444)
       put random(10) &cr after fld 1
     end repeat
     put cr&cr after fld 1
   end repeat
   --		
   -- Test 2: fixed randomSeed:
   repeat 2
     set the randomseed to 10
     repeat 10
       set the randomSeed to random(10)
       put random(10) &cr after fld 2
     end repeat
     put cr&cr after fld 2	
   end repeat
   --
end mouseUp


Results:

Field 1:
1 5 10 8 8 6 4 4 9 3
1 4 10 10 9 3 9 7 3 9


Field 2:
1 1 6 8 1 1 6 8 1 1
1 1 6 8 1 1 6 8 1 1


This seems to support the hypothesis that using a fixed randomSeed will 
result in the same sequence being generated even if you later set the 
randomSeed using random(), but changing the randomSeed to a non-fixed 
number changes the resulting sequence.

-- 
  Richard Gaskin
  Managing Editor, revJournal
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