Yes, you are right, I am trying to solve Oseen equation.<br><br>I tried using preconditioner PCILU(1) which works well.<br>But for PCILU(0) it did not work, as well as PCBJACOBI.<br>I have tried to insert zero on the diagonal, but it still does not work.
<br><br>In your opinion, what is the best parallel solver and preconditioner <br>for the Oseen equation ?<br><br>Thanks for your reply.<br>Liang<br><br><div><span class="gmail_quote">On 8/12/07, <b class="gmail_sendername">
Barry Smith</b> <<a href="mailto:bsmith@mcs.anl.gov">bsmith@mcs.anl.gov</a>> wrote:</span><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<br> It is not really the BiCGstab Krylov solver that it complaining;<br>it is the default ILU or block Jacobi with ILU on the blocks that is<br>complaining.<br><br> You first need to make sure you insert 0 entries on the all the diagonal
<br>entries that are 0. BUT given the structure of your matrix you may want<br>to think about solvers that specifically handle that type of matrix.<br><br> Barry<br><br>Stokes type solvers?<br><br><br>On Mon, 13 Aug 2007, Zhu Liang wrote:
<br><br>> By the way, the block of my matrix is like :<br>><br>> U , a<br>> A^T , 0<br>><br>><br>><br>> ---------- Forwarded message ----------<br>> From: Zhu Liang <<a href="mailto:liangcanada@gmail.com">
liangcanada@gmail.com</a>><br>> Date: Aug 13, 2007 5:46 AM<br>> Subject: How can I use BICGStab on a matrix with zero entries on the<br>> diagonal<br>> To: <a href="mailto:petsc-users@mcs.anl.gov">petsc-users@mcs.anl.gov
</a><br>><br>><br>> Dear petsc-users<br>><br>> When I try to solve a linear equation Ax=b with BicgStab preconditioner, I<br>> got<br>> an error "Matrix is missing diagonal number". That is because I have zeros
<br>> on<br>> the diagonal of the matrix.<br>><br>> I am wondering if there is some simple method to avoid that?<br>><br>> Best,<br>> Liang<br>><br><br></blockquote></div><br>