> On 01/04/2011, Gong Ding wrote: > > > > > Hi, > > > I am stiall dealing with the ill conditioned problem. :-( > > > Yesderday, I installed slepc-3.1-p6 for SVD calculation of my matrix. > > > > > > The SVD solver works well for the largest singualr value calculation. > > > But for the smallest singualr value, all most all the methods fail. > > > > > > Finally, I chosen the most inefficient way. > > > That build the cyclic matrix explicitly with > > > shift-and-invert spectral transformation. > > > And solve the eigen value problem by LU preconditioned GMRES. > > > The preconditioner should be superlu rather than others. > > > I guess the reason is superlu use static pivot. > > > Because solver with partial pivot such as mumps can not work. > > > Anyway, slepc solved my problem. > > > > > > However, the explicit building cyclic matrix takes too long to finish. > > > The log info says > > > > > > [0] MatSetUpPreallocation(): Warning not preallocating matrix storage > > > [0] MatAssemblyEnd_SeqAIJ(): Matrix size: 35038 X 35038; storage space: > > 325302 unneeded,482948 used > > > [0] MatAssemblyEnd_SeqAIJ(): Number of mallocs during MatSetValues() is > > 42204 > > > [0] MatAssemblyEnd_SeqAIJ(): Maximum nonzeros in any row is 33 > > > [0] Mat_CheckInode(): Found 26800 nodes of 35038. Limit used: 5. Using > > Inode routines > > > > > > It seems no preallocation for cyclic matrix. Is it a bug or I forgot > > something? > > > > > > > Yes, you are right. No preallocation is done in this case within SLEPc. This > is a problem also in SLEPc's QEPLINEAR. This is pending, my intention is to > get it fixed for the next release. >
Hope the problem can be solved soon. And do you have some comment on how to solve the smallest singular value? I guess i am not on the right way since matlab (with arpack) can calculate smallest singular value. But I never make arpack work. Even for smallest eigen value problem, arpack report no eigen value are found.
