[R] .Random.seed

[Prof Brian Ripley]

>From the NEWS for 1.8.0

    o   .Random.seed is only looked for and stored in the user's
        workspace.  Previously the first place a variable of that name
        was found on the search path was used.

Note that a local variable in a function was never used, so you are 
printing out a local variable .Random.seed which had nothing to do with 
random-number generation.

You need to save the value of .Random.seed from .GlobalEnv.


On Thu, 16 Oct 2003, Ann Hess wrote:

> I am writing a function for the purposes of a simulation.  Due to memory
> problems, the function sometimes crashes.  In order to get around this
> problem, I would like to include to be able to save the "last" seed, so I
> can pick up with the next run of the simulation after a "crash".  I am
> having trouble understanding what is going on with .Random.seed!
> 
> For each run of the following function, a random uniform and the current
> .Random.seed should be printed:
> 
> test<-function(runs,seed){
>    .Random.seed<-seed
>    for (i in 1:runs) {
> print(i)
> print(runif(1,0,1))
> print(.Random.seed)}
>    return(.Random.seed}
> 
> Consider the following input/output:
> >RNGkind(kind="Marsaglia-Multicarry")
> > set.seed(20391)
> > seed1<-.Random.seed
> > seed1
> [1]         401 -1607331462  -462081869
> > test(2,seed1)
> [1] 1
> [1] 0.4188851
> [1]         401 -1607331462  -462081869
> [1] 2
> [1] 0.7713649
> [1]         401 -1607331462  -462081869
> [1]         401 -1607331462  -462081869
> > seed1
> [1]         401 -1607331462  -462081869
> > test(2,seed1)
> [1] 1
> [1] 0.7293294
> [1]         401 -1607331462  -462081869
> [1] 2
> [1] 0.8266798
> [1]         401 -1607331462  -462081869
> [1]         401 -1607331462  -462081869
> 
> 
> The output from each call of the function seems to suggest that
> .Random.seed is not changing (although different random uniforms are
> generated each time).  The second call of the function doesn't match the
> first call even though the same "seed" is used.
> 
> Can anyone explain what is happening here?  My goal is to save the "last"
> seed so that I can use it to generate the next run of a simulation (after
> a crash).
> 
> Thanks in advance!
> 
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> 
> 

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595