<div dir="ltr"><div dir="ltr">On Mon, Dec 2, 2019 at 4:04 AM Li Luo <<a href="mailto:li.luo@kaust.edu.sa">li.luo@kaust.edu.sa</a>> wrote:<br></div><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr">Thank you for your reply.<div><br></div><div>The matrix is small with only 67500 rows, but is relatively dense since a second-order discontinuous Galerkin FEM is used, nonzeros=23,036,400.</div></div></blockquote><div><br></div><div>This is very dense, 0.5% fill or 340 nonzeros per row.</div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div>The number of colors is 539 as shown by using -mat_fd_coloring_view:</div></div></blockquote><div><br></div><div>Coloring is not appropriate for this matrix since you have enormous dense blocks (I am guessing). It could work if you statically</div><div>condense them out or had a fast analytic Jacobian. With 540 colors, it takes 540 matvecs to generate the action of the Jacobian.</div><div><br></div><div> Thanks,</div><div><br></div><div> Matt</div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div>MatFDColoring Object: 64 MPI processes<br> type not yet set<br> Error tolerance=1.49012e-08<br> Umin=1.49012e-06<br> Number of colors=539<br> Information for color 0<br> Number of columns 1<br> 378<br> Number of rows 756<br> 0 1188<br> 1 1188<br> 2 1188<br> 3 1188<br> 4 1188<br> 5 1188<br></div><div> ...</div><div><br></div><div>Is this normal?</div><div>When using MCFD, is there any difference using mpiaij and mpibaij?</div><div><br></div><div>Best,</div><div>Li</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Mon, Dec 2, 2019 at 10:03 AM Smith, Barry F. <<a href="mailto:bsmith@mcs.anl.gov" target="_blank">bsmith@mcs.anl.gov</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><br>
How many colors is it requiring? And how long is the MatGetColoring() taking? Are you running in parallel? The MatGetColoring() MATCOLORINGSL uses a sequential coloring algorithm so if your matrix is large and parallel the coloring will take a long time. The parallel colorings are MATCOLORINGGREEDY and MATCOLORINGJP<br>
<br>
Barry<br>
<br>
<br>
> On Dec 1, 2019, at 12:56 AM, Li Luo <<a href="mailto:li.luo@kaust.edu.sa" target="_blank">li.luo@kaust.edu.sa</a>> wrote:<br>
> <br>
> Dear Developers,<br>
> <br>
> I tried to use the multi-color finite-difference (MC-FD) method for constructing the Jacobians. However, I find it is very slow compared to the exact Jacobian. <br>
> My implementation of MC-FD Jacobian is posted below, would you please check whether I am correct? Anything missed? Thank you!<br>
> <br>
> ////////// Setup phase:<br>
> MatStructure flag;<br>
> ISColoring iscoloring;<br>
> ierr = MatGetColoring(Jac,MATCOLORINGSL,&iscoloring);<br>
> ierr = MatFDColoringCreate(Jac,iscoloring,&this->matfdcoloring);<br>
> ierr = MatFDColoringSetFunction(this->matfdcoloring,(PetscErrorCode (*)(void))__libmesh_petsc_snes_residual,(void *)this);<br>
> ierr = MatFDColoringSetFromOptions(this->matfdcoloring);<br>
> ierr = ISColoringDestroy(&iscoloring);<br>
> <br>
> //////////// Apply:<br>
> ierr = MatZeroEntries(*jac);CHKERRQ(ierr);<br>
> ierr = MatFDColoringApply(*jac,solver->matfdcoloring,x,msflag,snes);<br>
> <br>
> Best regards,<br>
> Li Luo<br>
> <br>
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