On Sat, Apr 19, 2014 at 2:13 PM, Umut Tabak <[email protected]> wrote:
> Dear all, > For any timing question, we need to see the output f -log_summary. Also, if you have significant time in routines you wrote, we need you to create PETSc events for these. Matt > I am experiencing lately some issues with a symmetric Lanczos eigensolver > in FORTRAN. Basically, I have test code in MATLAB where I am using > HSL_MA97(MATLAB interface) at the moment > > When I program Lanczos iterations in blocks in MATLAB by using HSL_MA97, > as expected my overall solution time decreases meaning that block solution > improves the solution efficiency. > > Then, to apply the same algorithm on problems on the orders of millions, I > am transferring the same algorithm to a FORTRAN code but this time with > MUMPS as the solver then I was expecting the solution time to decrease as > well, but my overall solution times are increasing when I increase the > block size. > > For a check with MUMPS, I only tried the block solution phase and compared > 120 single solutions to > > 60 solutions by blocks of 2 > 30 solutions by blocks of 4 > 20 solutions by blocks of 6 > 15 solutions by blocks of 8 > > and saw that the total solution time in comparison to single solves are > decreasing so I am thinking this is not the source of the problem, I > believe. > > What I am doing is that I am performing a full reorthogonalization in the > Lanczos loop, which includes some dgemm calls and moreover there are some > other calls for sparse symmetric matrix vector multiplications from Intel > MKL. > > I could not really understand why the overall solution time is increasing > with the increase of the block sizes in FORTRAN whereas I was expecting > even an improvement over my MATLAB code. > > Any ideas on what could be going wrong. > > Best regards and thanks in advance, > > Umut > -- 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
