[petsc-users] Why does CHOLMOD solution time differs between PETSc and MATLAB?

[Victor Magri]

Hi,

I'm solving a linear system which comes from the discretization of an
elliptic equation. The mesh has 1 million control volumes and there are two
more constraints for the system.

First, I've solved it in MATLAB using backslash command, which in turn
calls CHOLMOD once the matrix is SPD. Using tic and toc funtions, I could
see that it takes about 2s for the system to be solved (See attached for
more details).

I wrote both matrix and rhs in PETSc binary format and solved the linear
system using the example problem defined in ksp/examples/tutorials/ex10.c.
The command line options were:

mpiexec -n -1 ./ex10 -f A1mi.dat -rhs rhs1mi.dat -log_summary -ksp_monitos
-ksp_view -ksp_type preonly -pc_type cholesky -pc_factor_mat_solver_package
cholmod

The configuration parameters for CHOLMOD in PETSc and MATLAB seems the
same, so I was expecting a similar computation time, but it took about 13s
to solve in PETSc. (See attached for more details).

Why does CHOLMOD solution time differs between them?

If someone wants to try for yourself, here are the binaries for the matrix
and the rhs, respectively.
https://www.dropbox.com/s/q9s6mlrmv1qdxon/A1mi.dat?dl=0
https://www.dropbox.com/s/2zadcbjg5d9bycy/rhs1mi.dat?dl=0
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