Defining my own reordering method for ILU

[Barry Smith]

  Laslo,

   I would just "cheat" and compute the ordering up front and 
then just have it as a global variable that you access in the routine.

   The more "PETSc" way would be to use PetscObjectCompose to stick the
ordering you have computed in the matrix then PetscObjectQuery() to get
it out inside the MyOrdering routine.

   Barry

On Wed, 21 Feb 2007, Laslo Tibor Diosady wrote:

> Hi Barry,
> 
> If I understand how this works then I need to create a function 
> MatOrdering_MyOrdering(Mat mat,const MatOrderingType type,IS *irow,IS
> *icol)
> 
> My problem is that in order to compute my matrix ordering I need data
> other than the matrix as input. 
> 
> I can't see how I can do that if those are the only four arguments
> passed to the function.
> 
> Thanks,
> 
> Laslo
> 
> 
> 
> On Wed, 2007-02-21 at 11:27 -0600, Barry Smith wrote:
> >   Laslo,
> > 
> >    You can do your ordering up front to generate an index set.
> > But you will still need to write a routine MatOrdering_MyOrdering() that 
> > returns the isrow and iscol, then register the routine
> > with MatOrderingRegisterDynamic(). Then use PCFactorSetMatOrdering()
> > to tell the PC to use your new ordering routine. 
> > 
> > To have the preconditioner reuse the reordering for several matrices
> > use PCFactorSetReuseOrdering(). 
> > 
> >   Good luck,
> > 
> >    Barry
> > 
> > I know it is a little strange to need to provide the call back function
> > MatOrdering_MyOrdering() that simply returns the ordering you already
> > created but that is the only way to get the ordering into the right
> > place inside the PC objects.
> > 
> > The MatOrdering_MyOrdering() simply sets the isrow and iscol pointer
> > and returns.
> > 
> > On Wed, 21 Feb 2007, Laslo Tibor Diosady wrote:
> > 
> > > Hi,
> > > 
> > > I want to be able to define an ordering type for the ILU factorization
> > > to be used as a preconditioner to GMRES. I have successfully used
> > > PCFactorSetMatOrdering(), to set standard types, however I have my own
> > > reordering method which I would like to be able to use.
> > > 
> > > Since my reordering method is based on information not found within the
> > > matrix and I may want to solve several different systems with the same
> > > ordering, what I really want to be able to do is create an index set in
> > > advance and pass it is to be used for the reordering.
> > > 
> > > Is this possible, and how would you suggest I go about doing this?
> > > 
> > > Thanks,
> > > 
> > > Laslo
> > > 
> > > 
> > 
> 
>