adding SNESSetLinearSolve()

[Lisandro Dalcin]

Some time ago I made a request for adding SNESSetLinearSolve(), in
order to let users set a custom linear solve routine to SNES. I was
not clear to me if this idea was finally accepted, so I want to ask
again.

I really needs this feature in the near future, I I would like this to
go in the next petsc release. My use case is rather simple: I'm
helping a coworker to use SNES for solving a nonlinear optimization
problem related to mesh movement (that is, move nodes retaining
element connectivities). This problem uses a regularized functional,
wich introduces a global degree of freedom coupled with all others
dofs. To avoid assembling a sparse parallel AIJ matrix with a dense
column and row, we endup needing to solve two linear systems with the
same matrix for actually solving the Hessian of the regularized
functional.



-- 
Lisandro Dalcín
---------------
Centro Internacional de Métodos Computacionales en Ingeniería (CIMEC)
Instituto de Desarrollo Tecnológico para la Industria Química (INTEC)
Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)
PTLC - Güemes 3450, (3000) Santa Fe, Argentina
Tel/Fax: +54-(0)342-451.1594