Hi Barry Where can I find and use PCView_ICC ?
thanks Zhifeng Barry Smith wrote: > > On Sep 16, 2008, at 10:57 AM, zhifeng sheng wrote: > >> 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. > > I've added this information to PCView_ICC. > >> >> >> And when I solve it with KSP, the solver always complains about >> >> Detected zero pivot in Cholesky factorization >> >> How could it be? > > This is very possible, there is nothing that says you take some > symmetric matrix and do an ICC on it that you will get a positive > definite matrix or > no zero pivots. > > You can use -pc_factor_shift_positive_definite to force the ICC to > generate a positive definite matrix. > > Barry > >> >> >> 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 >>>> >>>> >>> >> >
