[petsc-users] Wrong answers from KSPSolve

Matthew Knepley petsc-maint at mcs.anl.gov
Tue Nov 6 16:02:43 CST 2012

On Tue, Nov 6, 2012 at 12:38 PM, NAN ZHAO <zhaonanavril at gmail.com> wrote:

> Dear all,
> I tried to solve a 18 by 18 linear system with KSPsolve, the right hand
> vector and matrix can be found in the file in the attachment. The right
> hand vector has several zeros and the corresponding row in the matrix only
> have values in diagonal, I expected zero at this element but got -1 for the
> answer. I am using the tutorial code
> in  petsc-3.2-p6/src/ksp/ksp/examples/tutorials/ex1.c as an example to
> assemble the matrix and vector and to solve the system. I also include the
> code in the attachment. I am working on a solution now but have run out of
> ideas.
> If you have any hint on the potential solution to this problems let me
> know.

There are just so many errors here its hard to begin:

  1) Your exact solution u does not match the rhs

  2) I changed b to match u

  3) The solver you chose was not solving the problem. The default works

Here is the fixed up code. Our job is not to debug your code.


> Thanks,
> Nan

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
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