On Tue, Sep 13, 2011 at 5:56 AM, Marco Cisternino <span dir="ltr"><<a href="mailto:marco.cisternino@polito.it">marco.cisternino@polito.it</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;">
Hi to everybody,<br>
I'm trying to solve this equation<br>
nabla(k*nabla(u))=f,<br>
with neumann homogeneous boundary conditions, where k is piecewise constant and f is a zero mean source (compatibility is respected).<br>
To do this I solve an extended by transmission conditions linear system, obtained with FD second order scheme.<br>
Everything works fine with dirichlet bc and with neumann bc too, if the interface, where k jumps, cut the computational domain.<br>
But if the interface is in the middle of the computational domain, something wrong happens where the processes overlap, with an overall loss of symmetry: the source, the interface and the bc are symmetric.<br>
I use gmres with asm. These are the lines to create the nullspace<br>
<br>
has_cnst=PETSC_TRUE<br>
call MatNullSpaceCreate(MPI_CART_<u></u>COMM,has_cnst,0,PETSC_NULL_<u></u>OBJECT,nsppoi,ierr)<br>
call KSPSetNullSpace(ksppoi,nsppoi,<u></u>ierr)<br>
<br>
Ask me everything you need to better understand the problem.<br>
Could you help me?<br></blockquote><div><br></div><div>If you have matrices, or submatrices, which must be symmetric, you can check this using</div><div><br></div><div> <a href="http://www.mcs.anl.gov/petsc/petsc-as/snapshots/petsc-current/docs/manualpages/Mat/MatIsSymmetric.html">http://www.mcs.anl.gov/petsc/petsc-as/snapshots/petsc-current/docs/manualpages/Mat/MatIsSymmetric.html</a></div>
<div><br></div><div> Thanks,</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;">
Thanks.<br>
<br>
Marco<br><font color="#888888">
<br>
-- <br>
Marco Cisternino<br>
PhD Student<br>
Politecnico di Torino<br>
<a href="mailto:Email%3Amarco.cisternino@polito.it" target="_blank">Email:marco.cisternino@polito.<u></u>it</a><br>
<br>
</font></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>