[petsc-users] Increasing norm with finer mesh

[Matthew Knepley]

On Mon, Oct 8, 2018 at 9:28 PM Weizhuo Wang <weizhuo2 at illinois.edu> wrote:

> The code is attached in case anyone wants to take a look, I will try the
> high frequency scenario later.
>

That is not the error. It is superconvergence at the vertices. The real
solution is trigonometric, so your
linear interpolants or whatever you use is not going to get the right value
in between mesh points. You
need to do a real integral over the whole interval to get the L_2 error.

  Thanks,

     Matt


> On Mon, Oct 8, 2018 at 7:58 PM Mark Adams <mfadams at lbl.gov> wrote:
>
>>
>>
>> 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).
>>
>>
>>>
>
> --
> 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/>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20181008/a1c8af0c/attachment.html>