Hi Prof. Wolfgang Bangerth,
I really appreciate for your quick reply. Now I do as what you said, using
VectorTools in setup_system(). It seems working, but there is still one
question that I always find very large values at points near boundaries,
see attached figures. Is there a way to solve this? Thanks for advance!
Have a nice day,
Mark
Code used as follows,
constraints.clear();
constraints.reinit(locally_relevant_dofs);
VectorTools::interpolate_boundary_values(dof_handler, BOUNDARY_NUM,
BoundaryValues_T<dim>(),constraints);
constraints.close();
Initial value projected by
VectorTools::project (dof_handler, constraints, QGauss<dim>(degree),
InitialValues_T<dim>(),
old_solution_T_cal);
<https://lh3.googleusercontent.com/-XqYsIGKYIy4/Wd0FDVsdz6I/AAAAAAAAACk/F0DTCvoewI8EiZg7JZs-Yp8KgUk7zaRhACLcBGAs/s1600/Screenshot%2Bfrom%2B2017-10-10%2B19-26-20.png>
<https://lh3.googleusercontent.com/-wW1-43huXAU/Wd0E4HHTDPI/AAAAAAAAACY/L6FBn5qtZQYcBmB5FkFsrwiUljvpLcfkgCLcBGAs/s1600/Screenshot%2Bfrom%2B2017-10-10%2B19-26-39.png>
After 30us, Temperature distribution
<https://lh3.googleusercontent.com/-Gr0uIEKJ8hk/Wd0FJmsv1nI/AAAAAAAAACs/P7nyohwFv0wk7_sQmdKB2NV4MWsFXq02gCLcBGAs/s1600/Screenshot%2Bfrom%2B2017-10-10%2B19-28-19.png>
<https://lh3.googleusercontent.com/-2qYzBzf0ADM/Wd0FH8B6YYI/AAAAAAAAACo/ByW7Hk66kHk5jOPhByZem7it3risRxPvgCLcBGAs/s1600/Screenshot%2Bfrom%2B2017-10-10%2B19-27-11.png>
在 2017年10月10日星期二 UTC+2下午5:48:57，Wolfgang Bangerth写道：
>
> On 10/10/2017 08:40 AM, Mark Ma wrote:
> >
> > I want to solve a heat equation in the time domain with distributed
> memory
> > using MPI, but the results are incorrect. In order to do so, I reference
> > tutorial step-23 for time updating method and step-40 for implementing
> MPI.
> > May I ask whether my boundary condition is right or not? Should we do
> > compress() after apply_boundary_values()? Thanks in advance!
>
> Jack -- how exactly is your solution wrong when you look at it? Do the
> boundary values look wrong? Are they correct if you run your MPI program
> with
> just one MPI process?
>
> In general, using MatrixTools::apply_boundary_values() is not the way to
> go
> with MPI programs. Rather, use a ConstraintMatrix and incorporate the
> boundary
> values into the same object as you do with hanging node constraints.
> That's
> what all of the parallel programs do, if I recall correctly.
>
> Best
> W.
>
> --
> ------------------------------------------------------------------------
> Wolfgang Bangerth email: [email protected]
> <javascript:>
> www: http://www.math.colostate.edu/~bangerth/
>
>
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