BLMVM doesn't use a KSP or preconditioner, it updates using the L-BFGS-B formula
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 >
