[petsc-users] KSP diverging

[Jed Brown]

On Fri, Dec 23, 2011 at 07:43, Matthew Knepley <knepley at gmail.com> wrote:

> Even if you lose orthogonality, it will just stagnate since you always
> have the solution
> from the first few vectors. Likewise, I do not see how you can get an
> diverging sequence
> from restarting since you always have the last residual, you just stagnate.
>

The true residual can grow even though the estimate of the preconditioned
residual decreases monotonically. When you restart, you re-evaluate the
actual residual, which might be much larger.
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