[petsc-users] Use block Jacobi preconditioner with SNES

[Stefano Zampini]

> Thanks for the answer. My system is sparse, and also a variable sized block matrix. For example, for a small size simulation, I have about 7K unknowns. For ONE TIME STEP, Intel MKL PARDISO took about 30 minutes to solve my system, while occupying about 2.5GB out of my 4GB RAM. Since I have to simulate at least 10000 time steps, the runtime (and the required RAM) would be unacceptable.
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This is very odd. A sparse linear system of 7K unknowns needs less than a second to be factored. If it is dense, seconds.
How many nonzero per rows do you have?
Is 7 thousand the typical size of your blocks in bjacobi?