[petsc-users] SuperLU convergence problem

[Danyang Su]

Dear All,

I got some strange solutions when using SuperLU for a complex reactive 
transport simulation. Before the timestep 28, everything works fine, for 
both sequential version and parallel version. Starting from timestep 29, 
the timestep cannot increase for SuperLU solver, for both sequential 
version and parallel version.

To check this problem, I dumped all the solutions using the sequential 
iterative solver (Step 1). Then I rerun this case using iterative solver 
(external solver, not from PETSc), SuperLU (from PETSc) and MUMPS (from 
PETSc) (Step 2). At every timestep and newton iteration, the solution is 
exported, and then the solution is replaced with the one from the 
sequential iterative solver from Step 1. In this case, all the matrices 
and rhs are identical for the three different solvers.

To my surprising, solutions from SuperLU at timestep 29 seems not 
correct for the first 4 Newton iterations, but the solutions from 
iteration solver and MUMPS are correct.

Please find all the matrices, rhs and solutions at timestep 29 via the 
link below. The data is a bit large so that I just share it through 
Dropbox. A piece of matlab code to read these data and then computer the 
norm has also been attached.
_https://www.dropbox.com/s/rr8ueysgflmxs7h/results-check.tar.gz?dl=0_

Below is a summary of the norm from the three solvers at timestep 29, 
newton iteration 1 to 5.

Timestep 29
Norm of residual seq 1.661321e-09, superlu 1.657103e+04, mumps 3.731225e-11
Norm of residual seq 1.753079e-09, superlu 6.675467e+02, mumps 1.509919e-13
Norm of residual seq 4.914971e-10, superlu 1.236362e-01, mumps 2.139303e-17
Norm of residual seq 3.532769e-10, superlu 1.304670e-04, mumps 5.387000e-20
Norm of residual seq 3.885629e-10, superlu 2.754876e-07, mumps 4.108675e-21

Would anybody please check if SuperLU can solve these matrices? Another 
possibility is that something is wrong in my own code. But so far, I 
cannot find any problem in my code since the same code works fine if I 
using iterative solver or direct solver MUMPS. But for other cases I 
have tested,  all these solvers work fine.

Please let me know if I did not write down the problem clearly.

Thanks,

Danyang



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