On Mon, Apr 2, 2012 at 11:33 AM, Xuefeng Li <li at loyno.edu> wrote: > On Mon, 2 Apr 2012, Matthew Knepley wrote: > > On Mon, Apr 2, 2012 at 10:11 AM, Xuefeng Li <li at loyno.edu> wrote: >> >> Hi, all. >>> >>> I am using multigrid with DMMG (5 levels) in my petsc program. >>> Turning on the dmmg_grid_sequence option seems >>> to slow down the program dramatically. For instance, >>> the program converges in 3 iterations in 6.270e+01 sec >>> when dmmg_grid_sequence is OFF; it also converges >>> in 3 iterations but in 1.699e+04 sec when dmmg_grid_sequence >>> is ON. >>> >>> Is this typical of petsc (I'm using petsc-3.1-p8)? >>> Are there ways to improve the performance when >>> dmmg_grid_sequence is ON? >>> >>> >> Its impossible to know what is happening from this description. There is >> no >> "generic" performance of grid sequencing. The best thing I can say to this >> is, >> it looks like the interpolated solution to your coarse problem is not a >> great >> solution to your fine problem. >> >> That is possible. > > > > However, you could be oversolving the coarse >> problems, blowing up the work, or interpolating badly for your problem. >> >> What do you mean by "oversolving the coarse problems"? > I am using the same stopping conditions in the two runs. >
Which may be too tight for the coarse runs. > The only difference is dmmg_grid_sequence ON and OFF. > > I also observed that in other situations, when dmmg_grid_sequence > is ON, the execution will abort due to "Out of memory" error, > whereas when OFF, the program converges without error. > How much more memory does grid-sequence employ? Twice as much? > If you use Galerkin MG, then t would depend on how full your Jacobian is. Matt > Regards, > > --Xuefeng Li, (504)865-3340(phone) > Like floating clouds, the heart rests easy > Like flowing water, the spirit stays free > http://www.loyno.edu/~li/home > New Orleans, Louisiana (504)865-2051(fax) > > -- 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 -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20120402/b6ef910c/attachment-0001.htm>
