<div dir="ltr"><div class="gmail_extra"><div class="gmail_quote">On Sun, Sep 25, 2016 at 4:06 AM, 丁老师 <span dir="ltr"><<a href="mailto:ztdepyahoo@163.com" target="_blank">ztdepyahoo@163.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div style="line-height:1.7;color:rgb(0,0,0);font-size:14px;font-family:arial"><div>Dear professor:</div><div>     In the ksp example ex50.c, i do not understand the meaning of </div><div><span style="font-family:monospace,consolas,"microsoft yahei";line-height:normal;white-space:pre-wrap;font-size:16px;color:rgb(0,0,0);text-decoration:underline"><u></u> <a href="http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/KSP/KSPSolve.html#KSPSolve" style="font-family:monospace,consolas,"microsoft yahei";line-height:normal;white-space:pre-wrap;font-size:16px;color:rgb(0,0,0);text-decoration:underline" target="_blank"><u>KSPSolve</u></a></span><span style="font-family:monospace,consolas,"microsoft yahei";line-height:normal;white-space:pre-wrap;font-size:16px;color:rgb(0,0,0)"><u>(ksp,NULL,NULL);</u></span></div><div><pre width="80" style="font-family:monospace,consolas,"microsoft yahei";font-size:medium;line-height:normal"><pre width="80" style="font-family:monospace,consolas,"microsoft yahei""><span style="color:rgb(0,0,0)"><u>     n</u></span><a href="http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Mat/MatNullSpaceCreate.html#MatNullSpaceCreate" style="text-decoration:underline;font-size:16px;color:rgb(0,0,0)" target="_blank"><span style="font-size:16px;color:rgb(0,0,0)"><u>MatNullSpaceCreate</u></span></a><span style="font-size:16px;color:rgb(0,0,0)"><u>(</u></span><a href="http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Sys/PETSC_COMM_WORLD.html#PETSC_COMM_WORLD" style="text-decoration:underline;font-size:16px;color:rgb(0,0,0)" target="_blank"><span style="font-size:16px;color:rgb(0,0,0)"><u>PETSC_<wbr>COMM_WORLD</u></span></a><span style="font-size:16px;color:rgb(0,0,0)"><u>,</u></span><a href="http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Sys/PETSC_TRUE.html#PETSC_TRUE" style="text-decoration:underline;font-size:16px;color:rgb(0,0,0)" target="_blank"><span style="font-size:16px;color:rgb(0,0,0)"><u>PETSC_TRUE</u></span></a><span style="font-size:16px;color:rgb(0,0,0)"><u>,0,0,&<wbr>nullspace);  </u></span></pre></pre></div><div>       What is the meaning of NULL in the kspsolve. <span style="font-size:14px;line-height:1.7">and two "0" in the </span><a href="http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Mat/MatNullSpaceCreate.html#MatNullSpaceCreate" style="font-family:monospace,consolas,"microsoft yahei";font-size:medium;line-height:normal;white-space:pre-wrap" target="_blank">MatNullSpaceCrea</a><span style="font-size:14px;line-height:1.7">te.</span></div></div></blockquote><div><br></div><div>1) The NULL for KSPSolve() means that </div><div><br></div><div>  <a href="http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/KSP/KSPSetComputeOperators.html">http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/KSP/KSPSetComputeOperators.html</a></div><div>  <a href="http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/KSP/KSPSetComputeRHS.html#KSPSetComputeRHS">http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/KSP/KSPSetComputeRHS.html#KSPSetComputeRHS</a></div><div><br></div><div>are used to make the problem.</div><div><br></div><div>2) The NullSpace is the space of constant functions with these arguments</div><div><br></div><div><br></div><div>  Matt</div><div><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 style="line-height:1.7;color:rgb(0,0,0);font-size:14px;font-family:arial"><div>Regards</div><div><div class="gmail-h5"><br><br><br> <br><div style="zoom:1"></div><div></div><br><pre><br>At 2016-09-24 00:25:09, "Jed Brown" <<a href="mailto:jed@jedbrown.org" target="_blank">jed@jedbrown.org</a>> wrote:
>"Kong, Fande" <<a href="mailto:fande.kong@inl.gov" target="_blank">fande.kong@inl.gov</a>> writes:
>
>> Any references on this topic except the users manual?  I am interested in
>> mathematics theory on this topic.
>
>These are relevant. I've only skimmed them briefly, but they might
>suggest ways to improve PETSc's handling of singular systems.  The
>technique is ancient.
>
><a href="https://doi.org/10.1137/S0895479803437803" target="_blank">https://doi.org/10.1137/<wbr>S0895479803437803</a>
>
><a href="https://doi.org/10.1007/s10543-009-0247-7" target="_blank">https://doi.org/10.1007/<wbr>s10543-009-0247-7</a>
</pre></div></div></div><br><br><span title="neteasefooter"><p> </p></span></blockquote></div><br><br clear="all"><div><br></div>-- <br><div class="gmail_signature">What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.<br>-- Norbert Wiener</div>
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