I think I may rephrase my problem like that, I have a huge matrix with n by n, at row m, I put a 1 in the location (m,m), other element in the row is zero. Then I construct a vector with size n, put zero in the m location. All other location I just put random number. I should get a answer vector with 0 in the mth element, But I some times got unreasonable number in this location. I am wondering if there is some option in petsc to avoid this case.
Thanks On Sat, Jun 25, 2011 at 2:58 PM, Matthew Knepley <knepley at gmail.com> wrote: > On Sat, Jun 25, 2011 at 2:49 PM, NAN ZHAO <zhaonanavril at gmail.com> wrote: > >> Dear all, >> >> I have a question about how to use the ksp in a smart way to solve a >> linear system. I had a simple test to generate a random matrix and vector, >> but I put only one nonzero value in a row (let's say 1), and in the respect >> location of the RHS vector I put a zero. The size of the matrix is kind of >> big, I saw petsc some time give unreasonable value at that loaction (it >> should be zero or some really small number). I want to know if there is a >> way to avoid it? >> > > The problem sounds degenerate. A full rank A with 1 nonzero/row and b = 0 > would not have a solution other than 0. What will this tell you? > > Matt > > >> Thanks >> > -- > What most experimenters take for granted before they begin their > experiments is infinitely more interesting than any results to which their > experiments lead. > -- Norbert Wiener > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20110625/4cc17284/attachment-0001.htm>
