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Date: Wed, 19 Jun 2024 16:49:33 -0400
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Subject: Re: Fortran, no RAN ?
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On 6/17/2024 7:49 PM, Arne Vajhøj wrote:
> But if RNDOM is REAL*4 then my guess would be:
> 
> RAN_LONGER_CYCLE(SEED1, SEED2)
> 
> Example:
> 
>        real*4 function ran2arg(seed1, seed2)
>        implicit none
>        integer*4 seed1, seed2
>        integer*4 temp
>        real*4 dummy
>        temp = xor(seed1, seed2)
>        ran2arg = ran(temp)
>        seed1 = xor(ishc(seed1, 1), temp)
>        seed2 = xor(ishc(seed2, -1), temp)
>        end
> 
> Disclaimer: I do not know if the cycle from this one is actual longer.

I did an experiment with start seeds 1234567 and 7654321.

I aborted after burning a little over 2 CPU hours.

No cycle detected after 1281 billion calls.

That doesn't prove that cycle will always be longer.

But it does not provide any basis for pessimism either.

Arne