[petsc-users] Differencing parameter works now

[Jed Brown]

On Tue, Mar 29, 2011 at 09:49, Kontsantinos Kontzialis <
ckontzialis at lycos.com> wrote:

> I have another question. I use the Discontinoues Galerkin discretization
> for the equations of gas dynamics. I use a matrix free formulation and
> that's why I need a very good preconditioner, which I compute it numerically
> and untill now it works ok, but it is a bit slow The preconditioner is just
> the Jacobian of the system. I wonder if PETSc has a built in capability to
> compute its entries.


You can use coloring, see snes/examples/tutorials/ex5.c for an example. It
is more expensive in 3D and if the stencil is large.
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