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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, I get -5, KSP_DIVERGED_BREAKDOWN, or maximum number of iterations exceeded.

What could be wrong? I am pretty sure my code is correct.

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ILU is not implemented for non-sequential matrices, see here.

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