[petsc-users] Increasing norm with finer mesh

[Mark Adams]

On Mon, Oct 8, 2018 at 6:58 PM Weizhuo Wang <weizhuo2 at illinois.edu> wrote:

> The first plot is the norm with the flag -pc_type lu with respect to
> number of grids in one axis (n), and the second plot is the norm without
> the flag -pc_type lu.
>

So you are using the default PC w/o LU. The default is ILU. This will
reduce high frequency effectively but is not effective on the low frequency
error. Don't expect your algebraic error reduction to be at the same scale
as the residual reduction (what KSP measures).


>
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