Hi Jed, I was searching a topic on preconditioning in the mail list and found this email.
On Wed, Oct 10, 2012 at 2:55 PM, Jed Brown <[email protected]> wrote: > Then you aren't using a matrix-free method at all. In case of using SNESDefaultComputeJacobianColor to compute Jacobian matrix and mf_operator command, is this exactly what you are describing ('aren't using a matrix-free method at all')? The SNESDefaultComputeJacobianColor I found in lines 149-155 from http://www.mcs.anl.gov/petsc/petsc-2.3.3/src/snes/examples/tutorials/ex5.c.html Best, Ling > Just don't call SNESSetJacobian and it will be done for you. Are you using > a DM? If not, you will also need to create a MatFDColoring. The easiest way > to do that, if you don't have a structured mesh, is to assemble the nonzero > pattern of your operator. > > > On Wed, Oct 10, 2012 at 3:44 PM, <[email protected]> wrote: > >> Is exactly the same. >> >> Kostas >> >> >> >> >> >> >> > On Wed, Oct 10, 2012 at 3:32 PM, <[email protected]> wrote: >> > >> >> Dear all >> >> >> >> I have a non-linear system which i want to solve it with matrix free >> >> method. However i must form the whole proconditioning matrix using >> >> finite >> >> differences and coloring method. >> >> >> > >> > How is the preconditioning matrix different from the actual operator? >> > >> > >> >> >> >> I can set the function F() of non-linear system (i take the notation >> F() >> >> from documentation). >> >> >> >> Could you send me exactly the commands and the order of it which i must >> >> use or an apt example for that? >> >> >> >> I have looked for that in internet but i could not find any suitable >> >> example. >> >> >> >> Kostas >> >> >> >> Thanks >> >> >> >> >> > >> >> >
