On Thu, Jun 18, 2015 at 1:52 PM, Jason Sarich <[email protected]> wrote:
> BLMVM doesn't use a KSP or preconditioner, it updates using the L-BFGS-B > formula > Then this sounds like a bug, unless one of the constants is partition dependent. Matt > On Thu, Jun 18, 2015 at 1:45 PM, Matthew Knepley <[email protected]> > wrote: > >> On Thu, Jun 18, 2015 at 12:15 PM, Jason Sarich <[email protected]> >> wrote: >> >>> Hi Justin, >>> >>> I can't tell for sure why this is happening, have you tried using quad >>> precision to make sure that numerical cutoffs isn't the problem? >>> >>> 1 The Hessian being approximate and the resulting implicit computation >>> is the source of the cutoff, but would not be causing different convergence >>> rates in infinite precision. >>> >>> 2 the local size may affect load balancing but not the resulting >>> norms/convergence rate. >>> >> >> This sounds to be like the preconditioner is dependent on the >> partition. Can you send -tao_view -snes_view >> >> Matt >> >> >>> Jason >>> >>> >>> On Thu, Jun 18, 2015 at 10:44 AM, Justin Chang <[email protected]> >>> wrote: >>> >>>> I solved a transient diffusion across multiple cores using TAO BLMVM. >>>> When I simulate the same problem but on different numbers of processing >>>> cores, the number of solve iterations change quite drastically. The >>>> numerical solution is the same, but these changes are quite vast. I >>>> attached a PDF showing a comparison between KSP and TAO. KSP remains >>>> largely invariant with number of processors but TAO (with bounded >>>> constraints) fluctuates. >>>> >>>> My question is, why is this happening? I understand that accumulation >>>> of numerical round-offs may attribute to this, but the differences seem >>>> quite vast to me. My initial thought was that >>>> >>>> 1) the Hessian is only projected and not explicitly computed, which >>>> may have something to do with the rate of convergence >>>> >>>> 2) local problem size. Certain regions of my domain have different >>>> number of "violations" which need to be corrected by the bounded >>>> constraints so the rate of convergence depends on how these regions are >>>> partitioned? >>>> >>>> Any thoughts? >>>> >>>> Thanks, >>>> Justin >>>> >>> >>> >> >> >> -- >> 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 >> > > -- 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
