[petsc-users] help on how to use petsc in a smart way

[Matthew Knepley]

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/20110625/463c361b/attachment.htm>