[petsc-users] about solving linear equation

[Jed Brown]

On Wed, Aug 24, 2011 at 14:11, Likun Tan <likunt at andrew.cmu.edu> wrote:

> I am solving a linear equation Ax=0 with Petsc.
> Previously i was following Numerical Recipe and using LU decomposition,
> for a non-singular matrix A, x should be zero. By applying LU in Recipe, i
> got x=0.
> When i solve it with ksp, x is some small value to the power of -9.
>

This is normal. You can make it more accurate by reducing the tolerance,
e.g. -ksp_rtol 1e-12.
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