<div dir="ltr"><div class="gmail_extra"><div class="gmail_quote">On Fri, Sep 23, 2016 at 9:38 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 style="line-height:1.7;color:rgb(0,0,0);font-size:14px;font-family:arial"><div style="line-height:1.7;color:rgb(0,0,0);font-size:14px;font-family:arial"><div style="line-height:1.7;color:rgb(0,0,0);font-size:14px;font-family:arial"><div style="line-height:1.7;color:rgb(0,0,0);font-size:14px;font-family:arial"><div style="line-height:1.7;color:rgb(0,0,0);font-size:14px;font-family:arial"><div style="line-height:1.7;color:rgb(0,0,0);font-size:14px;font-family:arial"><div style="line-height:1.7;color:rgb(0,0,0);font-size:14px;font-family:arial"><div>Dear friends:<br>     In the projection method for the solution of incompressible flow,  a pressure equation with four neuman bcs need to be solved. </div><div>but the pressure matrix is singular. it gives divergence solution.  how to solve this kind of equations.</div></div></div></div></div></div></div></div></div></blockquote><div><br></div><div>Tell the matrix it has a nullspace of constants:</div><div><br></div><div><a href="http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Mat/MatSetNullSpace.html">http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Mat/MatSetNullSpace.html</a><br></div><div><br></div><div>  Thanks,</div><div><br></div><div>    Matt</div><div> </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 style="line-height:1.7;color:rgb(0,0,0);font-size:14px;font-family:arial"><div style="line-height:1.7;color:rgb(0,0,0);font-size:14px;font-family:arial"><div style="line-height:1.7;color:rgb(0,0,0);font-size:14px;font-family:arial"><div style="line-height:1.7;color:rgb(0,0,0);font-size:14px;font-family:arial"><div style="line-height:1.7;color:rgb(0,0,0);font-size:14px;font-family:arial"><div style="line-height:1.7;color:rgb(0,0,0);font-size:14px;font-family:arial"><div style="line-height:1.7;color:rgb(0,0,0);font-size:14px;font-family:arial"><div>Regards</div></div><br><span title="neteasefooter"><p> </p></span></div><br><br><span title="neteasefooter"><p> </p></span></div><br><br><span title="neteasefooter"><p> </p></span></div><br><br><span title="neteasefooter"><p> </p></span></div><br><br><span title="neteasefooter"><p> </p></span></div></div><br><br><span title="neteasefooter"><p> </p></span></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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