Sylvain, Is there a reason you are not using Prometheus (--download_prometheus=1) for your MG preconditioner? It was designed with 3D solid mechanics in mind.
-sanjay On 5/11/11 11:12 PM, Sylvain Barbot wrote: > Dear Jed, > > During my recent visit to ETH, I talked at length about multi-grid > with Dave May who warned me about the issues of large > coefficient-contrasts. Most of my problems of interest for > tectonophysics and earthquake simulations are cases of relatively > smooth variations in elastic moduli. So I am not too worried about > this aspect of the problem. I appreciate your advice about trying > simpler solutions first. I have tested at length direct solvers of 2-D > and 3-D problems of elastic deformation and I am quite happy with the > results. My primary concern now is computation speed, especially for > 3-D problems, where i have of the order 512^3 degrees of freedom. I > was planning to test Jacobi and SOR smoothers. Is there another > smoother you recommend for this kind of problem? > > Thanks, > Sylvain > > 2011/5/11 Jed Brown<jed at 59a2.org>: >> On Wed, May 11, 2011 at 04:20, Sylvain Barbot<sylbar.vainbot at gmail.com> >> wrote: >>> I am still trying to design a >>> multigrid preconditionner for the Navier's equation of elasticity. >> I have heard, through an external source, that you have large jumps in both >> Young's modulus and Poisson ratio that are not grid aligned, including >> perhaps thin structures that span a large part of the domain. Such problems >> are pretty hard, so I suggest you focus on robustness and do not worry about >> low-memory implementation at this point. That is, you should assemble the >> matrices in a usual PETSc format instead of using MatShell to do everything >> matrix-free. This gives you access to much stronger smoothers. >> After you find a scheme that is robust enough for your purposes, _then_ you >> can make it low-memory by replacing some assembled matrices by MatShell. To >> realize most of the possible memory savings, it should be sufficient to do >> this on the finest level only.
