Coincidentally, Matt. I am gonna write the 2d heat dynamic problem.
Now I still not that much understand how DM mesh works.
It is a good chance to learn DM by studying your example.
Hope you the best!
David Jiawei LUO LIANG
南方科技大学/学生/研究生/2024
广东省深圳市南山区学苑大道1088号
------------------ Original ------------------
From: "Matthew Knepley"<knep...@gmail.com>;
Date: Thu, Nov 21, 2024 11:37 PM
To: "Jed Brown"<j...@jedbrown.org>;
Cc: "David Jiawei LUO LIANG"<12431...@mail.sustech.edu.cn>;
"petsc-users"<petsc-users@mcs.anl.gov>;
Subject: Re: [petsc-users] Cannot iterate well when using Newton
iteration of SNES
One more suggestion email. I solve the linear version myself in
ts/tutorials/ex45.c
Thanks,
Matt
On Thu, Nov 21, 2024 at 10:35 AM Jed Brown <j...@jedbrown.org> wrote:
You should add VecZeroEntries(f) near the top of your FormFunction (it's
currently accumulating into whatever was there last) and MatZeroEntries(B) to
FormJacobian.
I reduced to nElem = 5 for ease of viewing. With these changes, I see
quadratic convergence but the problem is still nonlinear. To explore further,
consider using these diagnostics
./SNES_heat -{snes,ksp}_monitor -{snes,ksp}_converged_reason
-snes_linesearch_monitor -ksp_view_mat
with and without -snes_fd.
For readability, I would suggest consistency in "u" vs "x".
"David Jiawei LUO LIANG"
<12431...@mail.sustech.edu.cn> writes:
> I am using the Newton iteration to solve a nonlinear 1D heat equation
problem by using FEM.
>
>
> I attached my source code named "SNES_heat.cpp"&nbsp;
>
>
> when I run the code
>
> &nbsp; 0 SNES Function norm 1.206289245288e+01
>
> &nbsp; 1 SNES Function norm 7.128802192789e+00
>
> &nbsp; 2 SNES Function norm 6.608812909525e+00
>
>
>
> you can find that it only iterate 3 steps, and then do all the function
evaluation and finally just stop the program.&nbsp;
>
>
> I think it is not reasonble. I check my code, it is correct if I set it
as a linear problem. it means my Jacobian and Residual function is correct.
>
>
> But when I set it as a nonlinear, the residual seems reduces as not
expected.&nbsp;
>
>
> I doubt that whether my understanding of the newton iteration is
different from SNES's newton iteration process.
>
>
>
>
>
>
>
>
> David Jiawei LUO LIANG
>
>
>
> 南方科技大学/学生/研究生/2024
>
>
>
> 广东省深圳市南山区学苑大道1088号
>
>
>
>
> &nbsp;
--
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
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