[petsc-users] A beginner question about a PETSc example

[Nan.Jia at Dartmouth.edu]

Hello all the PETSc users and developers,
I just started learning and exploring PETSc recently. I have a problem  
for the example: .../src/ksp/ksp/examples/ex2f.f
I run several times with different numbers of processors. Here are the  
results.

nan_jia at mir:/thayerfs/research/anatoly/NAN/Petsc/petsc-3.1-p8/src/ksp/ksp/examples/tutorials$ mpiexec -np 1 ./ex2f -m 100 -n  
100
Norm of error 0.8936E-02 iterations    65
nan_jia at mir:/thayerfs/research/anatoly/NAN/Petsc/petsc-3.1-p8/src/ksp/ksp/examples/tutorials$ mpiexec -np 2 ./ex2f -m 100 -n  
100
Norm of error 0.3148E-01 iterations    89
nan_jia at mir:/thayerfs/research/anatoly/NAN/Petsc/petsc-3.1-p8/src/ksp/ksp/examples/tutorials$ mpiexec -np 3 ./ex2f -m 100 -n  
100
Norm of error 0.3193E-01 iterations    92


What is weird to me is that with more processors, the norm does not  
decrease but increases, do does the number of iterations.

I also try to compare .../src/ksp/ksp/examples/ex2f.f with  
.../src/ksp/ksp/examples/ex1f.f  to see the difference between the  
sequential and parallel code in order to understand how PETSc  
parallelizes the code.

This is my first use the PETSc mailing list. Thanks everyone.

Best,
Nan