I'm solving $Ax = b$ with PETSc, $A$ sparse and asymmetric.
I'm using BCGS or FGMRES or TFQMR as a solver, and ILU as a preconditioner.
When I use 1 core, everything works as expected. But with 8 cores, no,
-5, KSP_DIVERGED_BREAKDOWN, or
maximum number of iterations exceeded.
What could be wrong? I am pretty sure my code is correct.