We are working on a general tool for adjoining PETSc-Code. Thats right -- the problem here is, that we can not store the complete history ( -- not necessarily a time stepping history, but rather the history of all computations) due to memory bounds.
As a case study we have a code calling the snes-solve(). -- And no time stepping at all. We want to skip storing all iteration steps etc. inside snes-solve() by exploiting exactly the fact that the solution is unique and satisfies f(x)=b. For doing so, we need to solve a linear system with the transposed Jacobian matrix of that corresponding snes-solve() later on. So in fact we only need to be able to solve this linear system with the jacobian at some point X_new with the same solution method used in the original snes-solve(). I thought the handiest approach was to store the SNES-struct. Johannes On 03/04/2013 06:11 PM, Barry Smith wrote: > On Mar 4, 2013, at 10:43 AM, Jed Brown <jedbrown at mcs.anl.gov> wrote: > >> On Mon, Mar 4, 2013 at 10:36 AM, Barry Smith <bsmith at mcs.anl.gov> wrote: >> So you save the solution at some time step. Then later in another part of >> the calculation, you time integrate the solution for a few time steps (from >> the saved time-step) to "fill in" the solution values you did not save, then >> you use the solutions for those several time steps, then you discard them. >> >> So the question has nothing to do with SNES. It has to do with a "deep >> copy" of TS? Or being able to "restart" TS at a saved time step? >> Capabilities we want to build towards, but thinking in terms of a deep copy >> of SNES is a red herring. >> >> Indeed, but presumably Johannes is working with an application that uses >> SNES. > Why would he be doing that? Surely it is better to use a TS integrator in > PETSc rather than to roll your own? If we were missing a feature needed for > his integrator from TS then we would gladly add it. > > Barry > >> >> >> So, assuming one is using a single time integrator (not changing the >> integration method for different times), shouldn't this already pretty much >> work? >> >> Yes, that's why I asked what sort of changes he was trying to guard against. >> Saving an entire copy of the SNES for each problem is wasteful when by far >> the most common case is to reuse configuration in each solve. > -- Dipl.-Ing. Johannes Lotz LuFG Informatik 12 der RWTH Aachen Software and Tools for Computational Engineering Room 0.25, S?sterfeldstr. 65, D-52072 Aachen Phone.: + 49 241 80 20127 mailto: lotz at stce.rwth-aachen.de http://www.stce.rwth-aachen.de
