[R] How to construct a valid seed for l'Ecuyer's method with given .Random.seed?

[Marius Hofert]

Since clusterSetupRNG() calls clusterSetupRNGstream() and this calls .lec.SetPackageSeed(), I could further minimalize the problem:

set.seed(1)
RNGkind("L'Ecuyer-CMRG") # => .Random.seed is of length 7 (first number encodes the rng kind)
(seed <- .Random.seed[2:7]) # should give a valid seed for l'Ecuyer's RNG
require(rlecuyer) # latest version 0.3-3
.lec.SetPackageSeed(seed)

The last line fails with:

,----
| Error in .lec.SetPackageSeed(seed) :
|   Seed[0] >= -767742437, Seed is not set.
`----

Looking at .lec.SetPackageSeed, "seed" seems to pass .lec.CheckSeed() [the check
could probably be improved here (but further checking is done in the C code; see
below)]:

,----
| > .lec.SetPackageSeed
| function (seed = rep(12345, 6))
| {
|     if (!exists(".lec.Random.seed.table", envir = .GlobalEnv))
|         .lec.init()
|     seed <- .lec.CheckSeed(seed) # => bad check since it's passed
|     .Call("r_set_package_seed", as.double(seed), PACKAGE = "rlecuyer") # => this fails!
|     return(seed)
| }
| <environment: namespace:rlecuyer>
`----

Going into the C code, r_set_package_seed calls RngStream_SetPackageSeed which in turn calls CheckSeed(seed). The relevant part of CheckSeed is this:

,----
| for (i = 0; i < 3; ++i) {
|     if (seed[i] >= m1) {
|     	/* HS 01-25-2012 */
|     	error("Seed[%1d] >= %d, Seed is not set.\n", i,m1);
|        /* original code
|          fprintf (stderr, "****************************************\n"
|       	 "ERROR: Seed[%1d] >= m1, Seed is not set.\n"
|       	 "****************************************\n\n", i);
|           return (-1);
|        */
|      }
| }
`----

Note that seed[0] in this (C-)code corresponds to the first element of my
variable "seed", which is -1535484873. This should definitely be smaller than m1
since m1 is defined as 4294967087.0 on line 34 in ./src/RngStream.c of the package 'rlecuyer'.

Why is seed[i] then >= m1??? This is strange. Indeed, as you can see from the
error message above, m1 is taken as -767742437 in my case (why?). Still (and even more
confusing), -1535484873 >= -767742437 is FALSE (!) but the if(){} is entered
anyways...


Cheers,

Marius