[petsc-users] Increasing norm with finer mesh

[Matthew Knepley]

On Mon, Oct 1, 2018 at 6:31 PM Weizhuo Wang <weizhuo2 at illinois.edu> wrote:

> Hi!
>
> I'm recently trying out the example code provided with the KSP solver
> (ex12.c). I noticed that the mean norm of the grid increases as I use finer
> meshes. For example, the mean norm is 5.72e-8 at m=10 n=10. However at
> m=100, n=100, mean norm increases to 9.55e-6. This seems counter intuitive,
> since most of the time error should decreases when using finer grid. Am I
> doing this wrong?
>

The norm is misleading in that it is the l_2 norm, meaning just the sqrt of
the sum of the squares of
the vector entries. It should be scaled by the volume element to
approximate a scale-independent
norm (like the L_2 norm).

  Thanks,

     Matt


> Thanks!
> --
> Wang Weizhuo
>


-- 
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

https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
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