Dear Barry I tried the RCM+ICC(2) in Petsc.... it seems that the reordering does not work well... as I view the preconditioner, it does not say in which way the matrix is reordered.
And when I solve it with KSP, the solver always complains about Detected zero pivot in Cholesky factorization How could it be? Thanks Best regards Zhifeng Barry Smith wrote: > > You should use rcm+icc if you want to keep a symmetric preconditioner. > > Depending on your matrix you might want to use KSPCR or KSPMINRES > or even KSPSYMMLQ > instead of bicgstab? > > We don't have a drop tolerance ICC and I do not recommend our drop > tolerance ILU. > > Barry > > > On Sep 16, 2008, at 10:23 AM, zhifeng sheng wrote: > >> Dear all >> >> I used the reordering scheme in petsc, and I would like to know >> whether they are symmetric or not. >> >> I have a symmetric matrix (for 3D system) and I tried to solve it >> with petsc and with matlab. >> >> In petsc I used rcm + ILU + bicgstab. while in matlab I used >> symrcm+ICC+bicgstab. >> >> it seems that with symmetric reordering, the factorization is >> somewhat faster... So I am wondering if it is possible to apply a >> symmetric reordering? >> >> PS: in Matlab, an incomplete factorization can be done with a >> tolerance (e.g. ICC(1e-4) ), can I do something like that with Petsc? >> >> Thanks a lot >> Best regards >> Zhifeng Sheng >> >> >
