[R] Help creating the IBM Randu function

[Huzefa Khalil]

Hi Martin,

The corrected function would be

RANDU <-  function(num) { return ((65539*num)%%(2^31)) }

You forgot the brackets for the return function.
Hence, what was returned was always (65539 * num)


On Mon, Aug 14, 2017 at 12:49 PM, Martin Møller Skarbiniks Pedersen
<traxplayer at gmail.com> wrote:
> Dear all,
>
>   I am trying to learn functions in R and 3D plotting so I decided to try
> to plot
> the famous bad PRNG Randu from IBM(1).
>    However something is not correct in the function I have created.
>    First I define the function RANDU like this:
>
>> RANDU <-  function(num) { return (65539*num)%%(2^31) }
>
> and test that it works for a seed of 1:
>> RANDU(1)
> [1] 65539
>
> but if I want the next value in the sequence I get this number.
>> (65539*65539)%%(2^31)
> [1] 393225
>
> However using the RANDU function twice doesn't give the same result as
> above.
>
>> RANDU(RANDU(1))
> [1] 4295360521
>
> I expect these two values to be the same but that is not the case.
> 393225 should be the correct.
>
> I guess it might be something with local vs. global environment ?!
>
> Please advise and thanks.
>
> Regards
> Martin M. S. Pedersen
>
> (1) https://en.wikipedia.org/wiki/RANDU
>
>         [[alternative HTML version deleted]]
>
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-- 
Huzefa Khalil
PhD Candidate,
Department of Political Science,
University of Michigan