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<div class="moz-cite-prefix">On 21.08.2012 18:14, Hong Zhang wrote:<br>
</div>
<blockquote
cite="mid:CAGCphBuwOKk+9C5Anv7AW-KW5TAoo0tN-xT2hpxCipk-RyumWQ@mail.gmail.com"
type="cite">Alexander :
<div><br>
<div>Testing your matrix A.dat
using petsc-3.3/src/ksp/ksp/examples/tutorials/ex10.c,</div>
<div>I find that A is numerically singular:</div>
</div>
</blockquote>
<br>
Hong,<br>
<br>
Sorry, but I forgot to mention that this is double complex symmetric
matrix. Did you load and treat it like that?<br>
<br>
<blockquote
cite="mid:CAGCphBuwOKk+9C5Anv7AW-KW5TAoo0tN-xT2hpxCipk-RyumWQ@mail.gmail.com"
type="cite">
<div>
<div>I'm convinced that matrix A is corrupted or obtained from
an incorrect numerical model.</div>
<div>Also note, your matrix A has size of approx. 60k, which is
too large for sequential direct solver.</div>
</div>
</blockquote>
<br>
MUMPS takes only several minutes and 6 GB of memory to factorize it.
<br>
This factorization gives residual on the order of 10e-12 and
solution is indeed correct.<br>
<br>
Nevertheless, you're right, there is numerical null-space in this
matrix since it comes <br>
from the discretization of equation that contains curl curl
operator, but practically this <br>
case is not really the worst one. <br>
<br>
<blockquote
cite="mid:CAGCphBuwOKk+9C5Anv7AW-KW5TAoo0tN-xT2hpxCipk-RyumWQ@mail.gmail.com"
type="cite">
<div>
<div>
<br>
</div>
<div>The error on MatMatSolve() when calling </div>
<div><span
style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13px;background-color:rgb(255,255,255)">' -pc_type
cholesky -pc_factor_mat_solver_package mumps'</span></div>
<div><span
style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13px;background-color:rgb(255,255,255)">is
a bug in our petsc-mumps interface. I've pushed a fix to
petsc-3.3</span></div>
<div><a moz-do-not-send="true"
href="http://petsc.cs.iit.edu/petsc/releases/petsc-3.3/rev/8badc49a596e">http://petsc.cs.iit.edu/petsc/releases/petsc-3.3/rev/8badc49a596e</a></div>
<div><br>
</div>
<div>Thanks for your report.</div>
</div>
</blockquote>
<br>
Thank you for the patch.<br>
<br>
<pre class="moz-signature" cols="72">--
Regards,
Alexander</pre>
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