[petsc-users] (no subject)

Smith, Barry F. bsmith at mcs.anl.gov
Mon Dec 2 01:03:34 CST 2019

  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


> On Dec 1, 2019, at 12:56 AM, Li Luo <li.luo at kaust.edu.sa> wrote:
> Dear Developers,
> 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. 
> My implementation of MC-FD Jacobian is posted below, would you please check whether I am correct? Anything missed? Thank you!
> ////////// Setup phase:
>           MatStructure flag;
>           ISColoring   iscoloring;
>           ierr = MatGetColoring(Jac,MATCOLORINGSL,&iscoloring);
>           ierr = MatFDColoringCreate(Jac,iscoloring,&this->matfdcoloring);
>           ierr = MatFDColoringSetFunction(this->matfdcoloring,(PetscErrorCode (*)(void))__libmesh_petsc_snes_residual,(void *)this);
>           ierr = MatFDColoringSetFromOptions(this->matfdcoloring);
>           ierr = ISColoringDestroy(&iscoloring);
> //////////// Apply:
>           ierr = MatZeroEntries(*jac);CHKERRQ(ierr);
>           ierr = MatFDColoringApply(*jac,solver->matfdcoloring,x,msflag,snes);
> Best regards,
> Li Luo
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