On Fri, Jun 21, 2019 at 8:07 AM Ale Foggia <amfog...@gmail.com<mailto:amfog...@gmail.com>> wrote: Thanks both of you for your answers,
El jue., 20 jun. 2019 a las 22:20, Smith, Barry F. (<bsm...@mcs.anl.gov<mailto:bsm...@mcs.anl.gov>>) escribió: Note that this is a one time cost if the nonzero structure of the matrix stays the same. It will not happen in future MatAssemblies. > On Jun 20, 2019, at 3:16 PM, Zhang, Junchao via petsc-users > <petsc-users@mcs.anl.gov<mailto:petsc-users@mcs.anl.gov>> wrote: > > Those messages were used to build MatMult communication pattern for the > matrix. They were not part of the matrix entries-passing you imagined, but > indeed happened in MatAssemblyEnd. If you want to make sure processors do not > set remote entries, you can use > MatSetOption(A,MAT_NO_OFF_PROC_ENTRIES,PETSC_TRUE), which will generate an > error when an off-proc entry is set. I started being concerned about this when I saw that the assembly was taking a few hundreds of seconds in my code, like 180 seconds, which for me it's a considerable time. Do you think (or maybe you need more information to answer this) that this time is "reasonable" for communicating the pattern for the matrix? I already checked that I'm not setting any remote entries. It is not reasonable. Could you send log view of that test with 180 seconds MatAssembly? Also I see (in my code) that even if there are no messages being passed during MatAssemblyBegin, it is taking time and the "ratio" is very big. > > > --Junchao Zhang > > > On Thu, Jun 20, 2019 at 4:13 AM Ale Foggia via petsc-users > <petsc-users@mcs.anl.gov<mailto:petsc-users@mcs.anl.gov>> wrote: > Hello all! > > During the conference I showed you a problem happening during MatAssemblyEnd > in a particular code that I have. Now, I tried the same with a simple code (a > symmetric problem corresponding to the Laplacian operator in 1D, from the > SLEPc Hands-On exercises). As I understand (and please, correct me if I'm > wrong), in this case the elements of the matrix are computed locally by each > process so there should not be any communication during the assembly. > However, in the log I get that there are messages being passed. Also, the > number of messages changes with the number of processes used and the size of > the matrix. Could you please help me understand this? > > I attach the code I used and the log I get for a small problem. > > Cheers, > Ale >
