When GSL PRNG + MPI used the same seed is used on all MPI ranks

[willfurnass]

$ mpirun ./main 5 its/0.xml | grep -i GSL
[GSL Random Number Generator] generator type: mt19937
[GSL Random Number Generator] seed = 1515443941
[GSL Random Number Generator] first value = 4052102787
[GSL Random Number Generator] generator type: mt19937
[GSL Random Number Generator] seed = 1515443941
[GSL Random Number Generator] first value = 4052102787
[GSL Random Number Generator] generator type: mt19937
[GSL Random Number Generator] seed = 1515443941
[GSL Random Number Generator] first value = 4052102787
[GSL Random Number Generator] generator type: mt19937
[GSL Random Number Generator] seed = 1515443941
[GSL Random Number Generator] first value = 4052102787

(using xparser commit ef57674)

Do people think it makes sense to have independent RNG streams per MPI rank?

If so, how about instead of the following (from the xparser-generated main.c):

gsl_seed = gsl_rng_default_seed;
gsl_seed = (unsigned long int) FLAME_environment_variable_GSL_RNG_SEED;
if(gsl_seed == 0) gsl_seed = gsl_rng_default_seed;
if(gsl_seed == 0) gsl_seed = (unsigned long int)time(NULL);
gsl_rng_set(FLAME_GSL_RNG, gsl_seed);

having something like

masterSeed = gsl_rng_default_seed;
masterSeed = (unsigned long int) FLAME_environment_variable_GSL_RNG_SEED;
if(gsl_seed == 0) {
    masterSeed = gsl_rng_default_seed;
if(gsl_seed == 0) {
    masterSeed = (unsigned long int)time(NULL);
}
#ifdef MPI_VERSION
/* Determine a rank-specific seed */
int rank;
unsigned int rankSeed;
err = MPI_Comm_rank(MPI_COMM_WORLD, &rank);
rankSeed = masterSeed + (unsigned int) rank
gsl_rng_set(FLAME_GSL_RNG, rankSeed);
#else 
gsl_rng_set(FLAME_GSL_RNG, masterSeed);
#endif

I would stick this the above in start_simulation() in the C source file containing my transition functions but FLAME_GSL_RNG is not in scope there.

[willfurnass]

(No idea why there are redundant lines in main.c BTW; no need for gsl_seed to be unconditionally assigned to twice then assigned to twice more if gsl_seed == 0; I'm just quoting what I found in my main.c).

[svdhoog]

@willfurnass I would offer such features as options to the user in some way. Either in the model.xml, or as options to switch on/off in the Makefile.templ (there could be a set of Makefile templates for different use-cases).