Hi, Thanks to Barry and Jed. I might come back later with few other questions. Amlan
On Wed, Dec 26, 2012 at 11:02 AM, Barry Smith <bsmith at mcs.anl.gov> wrote: > > On Dec 26, 2012, at 10:24 AM, Jed Brown <jedbrown at mcs.anl.gov> wrote: > > > On Wed, Dec 26, 2012 at 1:00 AM, amlan barua <abarua at iit.edu> wrote: > > Hi, > > Greetings to the team! I am currently using PETSc for my research. Here > is a brief description of my problem and my query > > a) I have a set a points distributed on a 3 dimensional lattice. > > b) Corresponding to each point in this set, 7 odes are defined. > > c) Of these 7 odes, 6 are uncoupled but one is coupled to nearest > neighbors. > > > > I suggest not optimizing for "missing" coupling to start with. We can do > the optimization in the solver, perhaps by splitting the DMDA into the > local and coupled parts. > > I agree with Jed here. Coincidently I am working on a similar problem > but with thousands of ODEs (mostly decoupled). You can use > DMDASetBlockFills(), the ofill parameter to indicate exactly what fields > are coupled to neighbors and which are not, this reduces the unneeded zero > Jacobian entries (you can also use the dfill parameter to reduce unneeded > zero entries in the 7 by 7 block). Eventually we'll use the same > information to reduce the ghost point communication also. > > Barry > > > > > d) To integrate the odes I am using PETSc's DMDA and TS. But my > application needs implicit as well as locally high order solver. I am > looking for an implicit RK4 type method. Does PETSc have an IRK4 support or > equivalent? > > > > If you are happy with a diagonally implicit method, you can use > TSARKIMEX (these integrators can be IMEX, but can also do any diagonally > implicit method). > > > > If you want a fully implicit RK (like Gauss, Radau IIA, etc) then all > stages are coupled together. Those methods are not currently implemented in > PETSc, though you could implement it either as a new TS implementation > (good for code reuse; you can do this outside of PETSc, but the code you > write is like library code) or manually using SNES (not reusable). > > > > e) Suppose I want to build my own implicit time stepper. Should I > imitate ex2.c of SNES solver? > > Thanks > > Amlan > > IISER Pune, India > > > > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20121226/dad400da/attachment.html>
