> On Mar 4, 2025, at 2:02 PM, Emmanuel Ayala <juan...@gmail.com> wrote:
>
> Hello everyone.
>
> I'm trying to solve a linear system (which comes from 3D FEM with structured
> DM mesh) with a direct solver. I configured petsc installation with mumps
> (–download-mumps –download-scalapack –download-parmetis –download-metis,
> --download-hwloc, without ptscotch) and I have the following functions:
>
> // K is the stiffness matrix, assembly correctly
> // U is the solution vector
> // RHS is the right hand side of the linear equation
>
> Mat Kfactor;
>
> ierr = MatGetFactor(K,MATSOLVERMUMPS, MAT_FACTOR_CHOLESKY, &Kfactor);
> CHKERRQ(ierr);
> ierr = MatCholeskyFactorSymbolic(Kfactor,K,0,0); CHKERRQ(ierr);
> ierr = MatCholeskyFactorNumeric(Kfactor,K,0); CHKERRQ(ierr);
> ierr = MatSolve(Kfactor,RHS,U);
Note 1) these four lines of code above are not needed if you use are using
KSPSolve to solve the system. The options below will trigger this.
>
> and run with options:
> -pc_type cholesky -pc_factor_mat_solver_type mumps -mat_mumps_icntl_1 1
> -mat_mumps_icntl_13 0 -mat_mumps_icntl_28 2 -mat_mumps_icntl_29 2
Note 2) it is imperative you use a good BLAS library and optimization when
using mumps. Do not use --download-blaslapack (or friends) and use
--with-debugging=0 in the configure option).
Note 3) If you are running sequentially (no MPI) then also ensure you have
--with-openmp in your configure options and set an appropriate value for the
number of OpenMP threads when you run your program.
>
> PROBLEM:
> I got the correct solution, but the function MatCholeskyFactorNumeric( )
> takes too much time to be completed. MatCholeskyFactorSymbolic() and
> MatSolve() are very fast. The test uses a square K matrix of 700k dofs, and
> the MatCholeskyFactorNumeric() takes around 14 minutes, while an iterative
> solver (KSPCG/PCJACOBI) takes 5 seconds to get the solution. Any suggestions?
>
> Thanks in advance.
