[petsc-dev] Copy *SNES-struct deeply

[Johannes Lotz]

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, Süsterfeldstr. 65, D-52072 Aachen
Phone.: + 49 241 80 20127
mailto: lotz at stce.rwth-aachen.de http://www.stce.rwth-aachen.de