<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 Jul 2022, at 2:32 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 Mon, Jul 11, 2022 at 1:17 PM Pierre Jolivet <<a href="mailto:pierre@joliv.et" class="">pierre@joliv.et</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">Hello,<br class="">
Could anyone help me understand what is going on in the following example, please?<br class="">
I have a VecNest.<br class="">
I either: a) initialize all values to 0.0, then set a specific part of the vector to nonzero or b) initialize a part of the vector to 0.0 and set the other part to nonzero.<br class="">
I don’t see why a) and b) produce different results.<br class="">
<br class="">
$ ./ex1111 -pc_type fieldsplit -ksp_monitor_true_residual -ksp_converged_reason -fieldsplit_pc_type jacobi -ksp_pc_side right -ksp_view_final_residual -nest_subvec true <br class="">
0 KSP unpreconditioned resid norm 8.375635517980e-01 true resid norm 8.375635517980e-01 ||r(i)||/||b|| 1.000000000000e+00<br class="">
1 KSP unpreconditioned resid norm 4.748816884247e-01 true resid norm 4.748816884247e-01 ||r(i)||/||b|| 5.669798875623e-01<br class="">
2 KSP unpreconditioned resid norm 4.713006778679e-01 true resid norm 4.713006778679e-01 ||r(i)||/||b|| 5.627043784990e-01<br class="">
3 KSP unpreconditioned resid norm 7.092979927129e-02 true resid norm 7.092979927129e-02 ||r(i)||/||b|| 8.468587144106e-02<br class="">
4 KSP unpreconditioned resid norm 1.457836310255e-02 true resid norm 1.457836310255e-02 ||r(i)||/||b|| 1.740567992870e-02<br class="">
5 KSP unpreconditioned resid norm 1.625040500524e-14 true resid norm 1.633468028779e-14 ||r(i)||/||b|| 1.950261595401e-14<br class="">
Linear solve converged due to CONVERGED_RTOL iterations 5<br class="">
KSP final norm of residual 1.63347e-14<br class="">
$ ./ex1111 -pc_type fieldsplit -ksp_monitor_true_residual -ksp_converged_reason -fieldsplit_pc_type jacobi -ksp_pc_side right -ksp_view_final_residual -nest_subvec false<br class="">
0 KSP unpreconditioned resid norm 0.000000000000e+00 true resid norm 8.375635517980e-01 ||r(i)||/||b|| inf<br class="">
Linear solve converged due to CONVERGED_ATOL iterations 0<br class="">
KSP final norm of residual 0.837564<br class=""></blockquote><div class=""><br class=""></div><div class="">I find if I assemble the vector, I get the same answers. Will try to figure out what assembly is doing.</div></div></div></div></blockquote><div><br class=""></div><div>It’s probably reseting all these values <a href="https://petsc.org/main/src/vec/vec/interface/rvector.c.html#line511" class="">https://petsc.org/main/src/vec/vec/interface/rvector.c.html#line511</a>, which I believe are being used in VecNorm() inside VecNormalize().</div><div>I guess any call to VecNestSubVec() should invalidate those as well, otherwise we get wrong cached norms.</div><div>I will give this a go.</div><div><br class=""></div><div>Thanks,</div><div>Pierre</div><br class=""><blockquote type="cite" class=""><div class=""><div dir="ltr" class=""><div class="gmail_quote"><div class=""> Thanks,</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">
Thanks,<br class="">
Pierre<br class="">
<br class="">
</blockquote></div><br clear="all" class=""><div class=""><br class=""></div>-- <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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