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On Fri, Mar 1, 2024 at 10: 28 AM Fabian Wermelinger <fab4100@ posteo. ch> wrote: Dear All, I am implementing a linear solver interface in a flow solver with support for PETSc. My application uses a parallel CSR representation and it manages
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<div dir="ltr"><div dir="ltr"><br></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Fri, Mar 1, 2024 at 10:28 AM Fabian Wermelinger <<a href="mailto:fab4100@posteo.ch">fab4100@posteo.ch</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div class="msg-8377303523939057983"><u></u>
<div style="font-size:1px;color:rgb(255,255,255);line-height:1px;height:0px;max-height:0px;opacity:0;overflow:hidden;display:none">
Dear All, I am implementing a linear solver interface in a flow solver with support for PETSc. My application uses a parallel CSR representation and it manages the memory for it. I would like to wrap PETSc matrices (and vectors) around it such
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<div><pre style="font-family:sans-serif;font-size:100%;white-space:pre-wrap">Dear All,
I am implementing a linear solver interface in a flow solver with support for
PETSc. My application uses a parallel CSR representation and it manages the
memory for it. I would like to wrap PETSc matrices (and vectors) around it such
that I can use the PETSc solvers as well. I plan to use
MatMPIBAIJSetPreallocationCSR and VecCreateMPIWithArray for lightweight
wrapping. The matrix structure is static over the course of iterations. I am
using a derived context class to host the PETSc related context. This context
holds references to the PETSc matrix and vectors and KSP/PC required to call the
solver API later in the iteration loop. I would like to create as much as
possible during creation of the context at the beginning of iterations (the
context will live through iterations).
My understanding is that MatMPIBAIJSetPreallocationCSR and VecCreateMPIWithArray
DO NOT copy such that I can wrap the PETSc types around the memory managed by
the hosting linear solver framework in the application. The system matrix and
RHS (the pointers to these arrays are passed to MatMPIBAIJSetPreallocationCSR
and VecCreateMPIWithArray, respectively) is assembled by the application before
any call to a linear solver.
Given this setting: for every iteration, my plan is the PETSc information from
the context (Mat, Vec, KSP) and simply call KSPSolve without any other PETSc
calls (still assuming the matrix structure is static during iteration).
What is not clear to me:
Are there any MatSetValues/VecSetValues calls followed by
MatAssembly/VecAssembly(Begin/End) calls required for this setting? </pre></div></div></blockquote><div>I don't believe so. </div><div>You are doing the assembly. </div><div>If you want to tell PETSc (KSP) that you changed the matrix so that it will re-setup the solvers (eg, refactor) then you can call KSPSetOperators.</div><div>(You might want to increment the state of the Mat so that other things like TS know the state has changed, maybe that is all that you need to do)</div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div class="msg-8377303523939057983"><div><pre style="font-family:sans-serif;font-size:100%;white-space:pre-wrap">The data in
the arrays for which pointers have been passed to MatMPIBAIJSetPreallocationCSR
and VecCreateMPIWithArray is computed prior to any solver call in an iteration,
such that I am assuming no additional "set value" calls through PETSc are
required -> am I missing something important by assuming this?</pre></div></div></blockquote><div>That sounds fine, but keep in mind that you need to use our data layout for the blocks if you use our MatVec, etc.</div><div><br></div><div>Thanks,</div><div>Mark</div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div class="msg-8377303523939057983"><div><pre style="font-family:sans-serif;font-size:100%;white-space:pre-wrap">Thank you for taking the time!
--
fabs
</pre></div>
</div></blockquote></div></div>