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

NAN ZHAO zhaonanavril at gmail.com
Fri Nov 2 09:15:28 CDT 2012

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.

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