Hello petsc-users and petsc-dev.
I am using PETSc to solve finite element problems. In particular I am
working with the dealii package which has C++ wrappers designed to
interface with PETSc. I am working on developing some of these
wrappers.
The difficulty I face is that, after applying boundary conditions
to the
matrices, these matrices return as nonsymmetric; I really need them
to be
symmetric! I can achieve this by performing the so-called Gauss
elimination step; however this requires access to the sparsity
pattern of
the PETSc matrix.
"The gauss elimination step "per se" is not a problem. The problem is
that we don't have access to the sparsity of the matrix, so it is not
so easy to find out which entries are not zero in the petsc matrices."
-- dealii developer
Is there *any* possible way to obtain the sparsity of the PETSc
matrix?
Maybe something like GetMatrixSparsity? I have done my research, but I
cannot find any information on this so I am pretty clueless on how
to proceed (sorry if I have missed something obvious).
Any comments or suggests would be greatly appreciated.
Best,
Toby
-----
Toby D. Young (Adiunkt)
Department of Computational Science
Institute of Fundamental Technological Research
Polish Academy of Science
Room 206, ul. Swietokrzyska 21
00-049 Warszawa, POLAND
Luca.
--
Luca Heltai <luca.heltai@xxxxxxxxx>
http://www-dimat.unipv.it/heltai
--
There are no answers, only cross references.
On Jun 15, 2007, at 11:17 AM, Toby D. Young wrote:
On Thu, 14 Jun 2007 10:55:20 -0400
Luca Heltai <luca.heltai@xxxxxxxxx> wrote:
Toby, if you do some serious development (like what you are
doing... :) ...) I strongly suggest you switch to the subversion
tree.
Okay, fair suggestion, and not too tricky to do, I'm running of
dealii
5.3pre now.
In the subversion tree that is implemented.
Yet it doesn't seem to be and the problem does not go away. I'll
have to
think of a way around this, either that or actually implement Guass
elimination for the Petsc SParseMatrix < scary thought :-) >.
You can verify this yourself by running step-17, after first changing
the final flag false->true in apply_boundary_conditions.
Here's what we find:
Cycle 0:
Number of active cells : 1024
Number of degrees of freedom : 1089 (by partition: 1089)
--------------------------------------------------------
An error occurred in line <534> of file
<source/numerics/matrices.all_dimensions.cc>
in function void dealii::PETScWrappers::apply_boundary_values(const
std::map<unsigned int, double, std::less<unsigned int>,
std::allocator<std::pair<const unsigned int, double> > >&,
PETScMatrix&, PETScVector&, PETScVector&, bool) [with PETScMatrix =
dealii::PETScWrappers::MPI::SparseMatrix, PETScVector =
dealii::PETScWrappers::MPI::Vector]
The violated condition was:
preserve_symmetry == false
The name and call sequence of the exception was:
ExcNotImplemented()
Additional Information:
(none)
Stacktrace:
-----------
#0 /home/tyoung/fem/deal.II/lib/libdeal_II_1d.g.so: void
dealii::PETScWrappers::apply_boundary_values<dealii::PETScWrappers::M
P
I::SparseMatrix,
dealii::PETScWrappers::MPI::Vector>(std::map<unsigned int, double,
std::less<unsigned int>, std::allocator<std::pair<unsigned int const,
double> > > const&, dealii::PETScWrappers::MPI::SparseMatrix&,
double> > > dealii::PETScWrappers::MPI::Vector&,
double> > > dealii::PETScWrappers::MPI::Vector&, bool)
double> > > #1 /home/tyoung/fem/deal.II/lib/libdeal_II_1d.g.so:
double> > > dealii::MatrixTools::apply_boundary_values
(std::map<unsigned
double> > > int, double, std::less<unsigned int>,
double> > > std::allocator<std::pair<unsigned int const, double> > >
double> > > const&, dealii::PETScWrappers::MPI::SparseMatrix&,
double> > > dealii::PETScWrappers::MPI::Vector&,
double> > > dealii::PETScWrappers::MPI::Vector&, bool)
#2 ./step-75: double> > > InfiniteWellProblem<2>::assemble_system()
#3 ./step-75: double> > > InfiniteWellProblem<2>::run()
#4 ./step-75: main
--------------------------------------------------------
--
Toby D. Young ( Adiunkt )
Department of Computational Science
Institute of Fundamental Technical Research, Polish Academy of
Sciences
Room 206, Swietokrzyska 21, 00-049 Warsaw, POLAND