On Fri, Mar 16, 2012 at 8:40 AM, Klaij, Christiaan <span dir="ltr"><<a href="mailto:C.Klaij@marin.nl">C.Klaij@marin.nl</a>></span> wrote:<br><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
The manual page 87 states that "there are several variants<br>
of the Schur complement preconditioner obtained by dropping some<br>
of the terms, these can be obtained with<br>
-pc_fieldsplit_schur_factorization_type <diag,lower,upper,full>"<br>
<br>
1) What is (will be) the name of the corresponding function?<br></blockquote><div><br></div><div>There isn't one.</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
2) It would be nice to know what exactly is being dropped. <full><br>
is obvious and apparently <diag> drops the right most matrix, but<br>
what do lower and upper drop?<br></blockquote><div><br></div><div><a href="http://www.mcs.anl.gov/petsc/petsc-dev/docs/manualpages/PC/PCFIELDSPLIT.html">http://www.mcs.anl.gov/petsc/petsc-dev/docs/manualpages/PC/PCFIELDSPLIT.html</a></div>
<div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
3) I'm confused about the minus sign in the <diag> form and its<br>
motivation. It doesn't come from the factorization. Is the rhs<br>
multiplied with a minus sign as well? Why not follow the sign<br>
convention of Elman's taxonomy (eq 3 and 4, JCP 227, 2008)?<br></blockquote><div><br></div><div>It makes the PC positive definite.</div><div><br></div><div> Matt</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<br>
dr. ir. Christiaan Klaij<br>
CFD Researcher<br>
Research & Development<br>
E mailto:<a href="mailto:C.Klaij@marin.nl">C.Klaij@marin.nl</a><br>
T <a href="tel:%2B31%20317%2049%2033%2044" value="+31317493344">+31 317 49 33 44</a><br>
<br>
MARIN<br>
2, Haagsteeg, P.O. Box 28, 6700 AA Wageningen, The Netherlands<br>
T <a href="tel:%2B31%20317%2049%2039%2011" value="+31317493911">+31 317 49 39 11</a>, F <a href="tel:%2B31%20317%2049%2032%2045" value="+31317493245">+31 317 49 32 45</a>, I <a href="http://www.marin.nl" target="_blank">www.marin.nl</a><br>
<br>
</blockquote></div><br><br clear="all"><div><br></div>-- <br>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<br>