[petsc-users] small number (1e-23) in the matrix

[Matthew Knepley]

On Fri, Nov 2, 2012 at 10:15 AM, NAN ZHAO <zhaonanavril at gmail.com> wrote:

> Dear all,
>
> I am using PETSC to solve a nonlinear system with newton's method. I
> actually calculate the jacobian matrix in each newton iteration and solve
> the linear system by KSPsolve. However, I found one thing
> really brothers me is the ultra small numbers in the matrix (MPIBAIJ
> matrix). In the sparse matrix I create some location should be zero but I
> got some small values like 1e-23 instead. I use matzeroentries each time I
> give new value to the matrix and this problem still exist. What makes me
> more confuse is that if I do not use matzeroentries each time I give new
> values to the matrix, the locations which should be zero get exactly
> 0.0000e0 (although other values is wrong, cause I add new value to the
> location when I assemble the matrix, I can not use insert as the procedure
> is like finite element assembling). Does anyone have insight of why this
> happens? P.S. I tried destroy the matrix each time I give the new value but
> same thing happens.
>

You are not doing what you think you are doing. This has nothing to do with
MatZeroEntries(). You are inserting
weird values in the matrix, probably by misspecifying a length, so that
MatSetValues() reads off the end of an
array. Run your code through valgrind.

   Matt


> Regards,
> 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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