On Fri, Aug 28, 2015 at 6:02 AM, Mark Adams <[email protected]> wrote: > Is there a good way to get a deterministic rand wrt number of processors? > Seeding rand for each entry, with its global ID would work I assume. > > If drand48 is just one line then why not just copy it tweak it as desired? >
I did. Its in next. Matt > Cheby is otherwise deterministic, with a deterministic PC, and we have > equation numbers to make this work. Eigen estimates are a real pain and the > source of a lot of time consuming AMG errors. It would be nice to have it > not depend in any way on processor count. > > On Thu, Aug 27, 2015 at 10:12 PM, Barry Smith <[email protected]> wrote: > >> >> > On Aug 27, 2015, at 5:35 PM, Jed Brown <[email protected]> wrote: >> > >> > Barry Smith <[email protected]> writes: >> >> This is the default behavior if one just creates a PetscRandom and >> uses it, so don't be going and setting seeds inside GAMG or Chebyshev. >> > >> >> Yikes, you are right all three of our current random number generators >> have global state! What a mess. We should remove all them completely and we >> can complement Matt's by adding in a more modern version of Sprng that does >> not use global state. (Stupid Sprng fucks changed to C++) >> >> Barry >> >> > You're right (my mistake), but the consequences are dangerous if the >> > user is holding a PetscRandom across calls to GAMG (or anything that >> > creates new PetscRandom instances). The reason is that merely creating >> > a PetscRandom reseeds the global PRNG. (What moron thought a global >> > seed was a good idea?) Seems to me we should avoid drand48 always so we >> > don't disrupt the user's source of randomness (leading to really >> > confusing incorrect results). We could use the non-disastrous >> > drand48_r, but it's a GNU extension so we'd need an alternative anyway. >> > >> > If Matt changes "rander48" to the rand48_r (or erand48_r) interface, >> > then we'd be okay. This would also remove the internal variables that >> > Matt forget to make static. >> >> > -- What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead. -- Norbert Wiener
