[petsc-dev] use of random numbers in GAMG

[Barry Smith]

  Mark,

    So GAMG uses random numbers in the implementation, this means identical runs on machines with different random number generates can produce noticeable different convergence histories. This means that the "no change" tests in the nightly tests indicate change (i.e. a problem) when this perhaps not a problem. So it is impossible to trust the results of the tests.

   Is there anything we can do to alleviate this problem? Are the random number usage fundamental to the algorithm? Should we distribute with PETSc a "random number generator" that will generate the same results on all systems (if that is even possible?)?

  Thanks

  Barry


Note that on the same machine if you run the same program twice with our default system provided "random number generator" you will get the same result, this is an issue with running on different kinds of machines and getting different results.