[Rd] Bias in R's random integers?

[Radford Neal]

> From: Duncan Murdoch <murdoch.duncan using gmail.com>

> Let's try it:
> 
>  > m <- (2/5)*2^32
>  > m > 2^31
> [1] FALSE
>  > x <- sample(m, 1000000, replace = TRUE)
>  > table(x %% 2)
> 
>       0      1
> 399850 600150
> 
> Since m is an even number, the true proportions of evens and odds should 
> be exactly 0.5.  That's some pretty strong evidence of the bug in the 
> generator. 


It seems to be a recently-introduced bug.  Here's output with R-2.15.1:

  R version 2.15.1 (2012-06-22) -- "Roasted Marshmallows"
  Copyright (C) 2012 The R Foundation for Statistical Computing
  ISBN 3-900051-07-0
  Platform: x86_64-unknown-linux-gnu (64-bit)
  
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  Type 'license()' or 'licence()' for distribution details.
  
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  > set.seed(123)
  > m <- (2/5)*2^32
  > m > 2^31
  [1] FALSE
  > x <- sample(m, 1000000, replace = TRUE)
  > table(x %% 2)
  
       0      1 
  499412 500588 
  
So I doubt that this has anything to do with bias from using 32-bit
random values.

   Radford Neal