Hi,
I am trying to do LU factorization to an ill-conditioned system. PETSc gives me
"Detected zero pivot in LU factorization". The problem is solved when I use
PCFactorSetShiftNonzero.
Just to be sure, I used Matlab and Lapack(DGETRF) to do the factorization. They
did it without any complain and they gave me the same answer. However, the
answer I got from PETSc is completely different.
In PETSc I did the following:
????? call KSPCreate(PETSC_COMM_SELF,ksp1,ierr)
????? call KSPSetOperators(ksp1,PSASTF,PSASTF,SAME_NONZERO_PATTERN,ierr)
????? call KSPSetType(ksp1,KSPPREONLY,ierr)
????? call KSPGetPC(ksp1,prec1,ierr)
????? call PCSetType(prec1,PCLU,ierr)
????? call PCFactorSetShiftNonzero(prec1,PETSC_DECIDE,IERR)
????? call KSPSetFromOptions(ksp1,ierr)
????? call KSPSetUp(ksp1,ierr)
Any idea why PETSc gives different answer than Matlab and Lapack routine
(DGETRF).
Thanks
Waad
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