Re: MatZeroColsIS question.

[Peter Schröder <ps@xxxxxxxxxxxxxx>]

Lisandro Dalcin wrote:

On 9/4/07, Peter Schröder <ps@xxxxxxxxxxxxxx> wrote:
  

Why not just construct the matrix without the corresponding columns and
rows? That preserves the symmetry (as it should of course), gives you a
smaller matrix, and you don't have the hassle with the zero columns.
    

The former is far simpler in some contexts, and the size (of the
matrix) is not an issue if the appropriate MatOption is set regarding
sucessive assemblies.
  

Yes. And of course I didn't really answer the original question...

I was discussing on petsc-dev about implementing a general object
PetscMapping. This would enable to set a general mapping on Vec's and
Mat's for using with {Vec|Mat}SetValues in order to 'filter and map'
indices, but this is a non-trivial feature that will require a fair
amount of time to implement.

Such a thing could be very valuable. For example in active set methods... I just ran into that and gave up (turns out that I was lucky in that the Legendre dual of my energy is without constraints).

Peter