On Sun, Nov 17, 2013 at 1:42 PM, Subramanya Sadasiva <[email protected]>wrote:
> Hi, > I am trying to solve a degenerate cahn hilliard inequality using petsc_DM > and virs through libmesh. The problem is that the jacobian for this system > has a nearly singular block owing to the \delta t term multiplying the K > > [ K + M M ] [ \delta phi] = -R_phi > [ M K deltat] [\delta mu ] = -R_mu > > This leads to the unfortunate situation that the time stepping actually > fails for very small timesteps. a solution that seems possible is to add a > constant mass matrix to the K delta t, making the system > > [ K + M M ] [ \delta phi] = -R_phi > [ M K deltat +M] [\delta mu ] = -R_mu + M \delta mu > > And using the \delta mu from the previous timestep. I was just wondering > if there is any way to get the pre-line search value of the \delta mu? Is > it okay to get the \alpha from the linesearch and divide the previous > change by the \alpha? > Why wouldn't you just scale the problem (Jacobi)? Matt > I hope I am making sense here. > Thanks, > Subramanya > > > -- What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead. -- Norbert Wiener
