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 bounda
Toby,
If I understand you correctly, a trick we use for this is to use
MatGetRow to get the sparcity pattern of each row (where you are
applying BCs) and then create a vector of zeros and use MatSetValues
using the *row* sparcity from MatGetRow and SET the *column* values
with this vector
> If I understand you correctly, a trick we use for this is to use
> MatGetRow to get the sparcity pattern of each row (where you are
> applying BCs)
Neat trick. MatGetRow will give me the row of the matrix, so would then
need a little loop to examine the elements and proceed as you suggested;
a
>
> Neat trick. MatGetRow will give me the row of the matrix, so would
> then
> need a little loop to examine the elements and proceed as you
> suggested;
> am I right?
>
There is probably more than one way to do this but you do NOT need to
look at the elements (you can give PETSc a NULL arg
Toby,
For Seq matrices you can call MatGetRowIJ() and it will give
you exactly what you want. For MPI matrices the matrices are stored
in two parts on each process (the "diagonal" part and the "off-diagonal" part)
you can, of course, call the MatGetRowIJ() on each part but this is
not exact
Barry,
Thank you for an interesting response.
> For algorithms that require dealing with the sparsity structure of
> the matrix we generally just include the appropriate private include file
> for the matrix format and access the data directly in the underlying format.
Can you please elabora
src/mat/impls/aij/seq/aij.h
src/mat/impls/aij/mpi/mpiaij.h
On Fri, 15 Jun 2007, Toby Young wrote:
>
>
> Barry,
>
> Thank you for an interesting response.
>
> > For algorithms that require dealing with the sparsity structure of
> > the matrix we generally just include the appropriate
Just a note, my way is much simpler - its two lines of code in a loop
over the boundary nodes, followed by an MatAsseblyBegin/End, and you
don't have to deal with parallel issues explicitly - PETSc does. For
my FE codes the cost of this (dumb) way is negligible, PETSc
implements these meth
Also, I have talked to Wolfgang many times about this. I am a firm
believer in eliminating the boundary values during assembly at the
element level. PETSc provides an easy mechanism for this. By default,
all negative indices in calls to VecSetValues and MatSetValues are
ignored.
Matt
On 6/15/07
