On Fri, Apr 8, 2011 at 11:40, <domenico.borzacchiello at univ-st-etienne.fr>wrote:
> I can't get why it takes more than one Newton iteration even if my system > is linear and the linear solver is direct. > The direct solver should also converge in one iteration. Are you only assembling an approximation of the Jacobian (e.g. using -snes_mf_operator)? If using MFFD, is the system poorly scaled such that the step size is very low accuracy (maybe try -mat_mffd_type ds)? Are the equations singular? Is both the Jacobian and residual evaluation correct? > > As for the Vanka smoother would you suggest to implement it with PCSHELL > or by defining a new PC type? > That is up to you. Defining a new PC type makes it more reusable, but PCShell is a bit quicker to develop. You can start with PCShell and convert it later. -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20110408/18d74b06/attachment-0001.htm>
