A different kind of lagged preconditioner

[Barry Smith]

On Mar 23, 2009, at 2:06 PM, Rafael Santos Coelho wrote:

> Barry,
>
> sorry if I'm coming off stubborn or something, but I think I'm not  
> following your reasoning.
>
>  NO.
>
>  If you are using LU to construct a preconditioner then you ARE  
> providing the Jacobian explicitly (as a sparse) matrix.  Each time  
> the preconditioner is built this sparse matrix is factored.
>
> What do you mean by "providing the jacobian explicity (as a sparse)  
> matrix"? I thought that there was no explicit jacobian matrix, but  
> only a MATMFFD context.

   If so, then you are not using LU as a preconditioner; in fact you  
are not using a preconditioner at all. Run with -snes_view and send us  
the output to see what solver you are actually using.


>
>
> Rafael