<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><br class=""><div><br class=""><blockquote type="cite" class=""><div class="">On 12 Mar 2020, at 11:40 PM, Matthew Knepley <<a href="mailto:knepley@gmail.com" class="">knepley@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class=""><div dir="ltr" class="">On Thu, Mar 12, 2020 at 5:59 PM Jed Brown <<a href="mailto:jed@jedbrown.org" class="">jed@jedbrown.org</a>> wrote:<br class=""></div><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Pierre Jolivet <<a href="mailto:pierre.jolivet@enseeiht.fr" target="_blank" class="">pierre.jolivet@enseeiht.fr</a>> writes:<br class="">
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> Hello,<br class="">
> Has there been any follow-up on this <a href="https://lists.mcs.anl.gov/pipermail/petsc-users/2015-January/024020.html" rel="noreferrer" target="_blank" class="">https://lists.mcs.anl.gov/pipermail/petsc-users/2015-January/024020.html</a> <<a href="https://lists.mcs.anl.gov/pipermail/petsc-users/2015-January/024020.html" rel="noreferrer" target="_blank" class="">https://lists.mcs.anl.gov/pipermail/petsc-users/2015-January/024020.html</a>>?<br class="">
> Given a 3x3 MatNest A = [A_00,0,0 ; 0,A_11,0 ; 0,0,A_22], I’d like to setup a two-way fieldsplit coupling [A_00,0 ; 0,A_11] and [A_22] but I can’t figure out the proper options.<br class="">
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Are you looking for a Schur split or additive/multiplicative?</blockquote></div></div></div></blockquote><div><br class=""></div><div>Don’t know yet which will perform best, do you have a specific solution in mind for one scenario or the other?</div><div>I was mostly wondering if it was possible in a general context, not taking -pc_fieldsplit_type into account.</div><br class=""><blockquote type="cite" class=""><div class=""><div dir="ltr" class=""><div class="gmail_quote"><div class="">-pc_fieldsplit_field_0 0,1 -pc_fieldsplit_field_1 2 -pc_fieldsplit_type schur</div></div></div></div></blockquote><div><br class=""></div><div>These flags, used with my .cpp, yield:</div><div><div>[0]PETSC ERROR: Arguments are incompatible</div><div>[0]PETSC ERROR: To use Schur complement preconditioner you must have exactly 2 fields</div><div>If I use -pc_fieldsplit_%d_fields <a,b,..> as advocated in the manual (instead of -pc_fieldsplit_field_%d as you suggested), I get the same error.</div></div><br class=""><blockquote type="cite" class=""><div class=""><div dir="ltr" class=""><div class="gmail_quote"><div class="">I believe.</div><div class=""><br class=""></div><div class=""> Matt</div><div class=""> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
> Jed, in this answer <a href="https://lists.mcs.anl.gov/pipermail/petsc-users/2015-January/023993.html" rel="noreferrer" target="_blank" class="">https://lists.mcs.anl.gov/pipermail/petsc-users/2015-January/023993.html</a> <<a href="https://lists.mcs.anl.gov/pipermail/petsc-users/2015-January/023993.html" rel="noreferrer" target="_blank" class="">https://lists.mcs.anl.gov/pipermail/petsc-users/2015-January/023993.html</a>>, you recommend not to use MatNest. What would you recommend instead?<br class="">
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See src/snes/examples/tutorials/ex28.c for my preferred approach.</blockquote></div></div></div></blockquote><div><br class=""></div><div>I’m not using DM, so in terms of Mat, I guess this example shows that I pretty much need to reimplement the field splitting myself?</div><div><br class=""></div><div>Thanks,</div><div>Pierre</div><br class=""><blockquote type="cite" class=""><div class=""><div dir="ltr" class="">-- <br class=""><div dir="ltr" class="gmail_signature"><div dir="ltr" class=""><div class=""><div dir="ltr" class=""><div class=""><div dir="ltr" class=""><div class="">What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.<br class="">-- Norbert Wiener</div><div class=""><br class=""></div><div class=""><a href="http://www.cse.buffalo.edu/~knepley/" target="_blank" class="">https://www.cse.buffalo.edu/~knepley/</a><br class=""></div></div></div></div></div></div></div></div>
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