<html><head><meta http-equiv="Content-Type" content="text/html; charset=us-ascii"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">"Solve the forward problem" means "solve the Stokes equations". This terminology is used to contrast with the "inverse problem" of recovering the parameters of the Stokes equations (viscosity) from the solution (pressure and velocity). <div class=""><br class=""></div><div class="">Here, it sounds like you need to be able to </div><div class="">1) solve the (discretized) Stokes equations (see Matt's comments)</div><div class="">2) use SLEPc to analyze the operator (in PETSc, a "Mat" object) and extract the eigenvalues.<br class=""><div><br class=""><blockquote type="cite" class=""><div class="">Am 29.10.2019 um 13:58 schrieb alex via petsc-users <<a href="mailto:petsc-users@mcs.anl.gov" class="">petsc-users@mcs.anl.gov</a>>:</div><br class="Apple-interchange-newline"><div class=""><div class="">Sorry, perhaps I stated my problem a bit inaccurately and that may have caused misunderstanding. In fact, I need to solve the forward problem, i.e. I have to find eigenvalues for the three dimensional Stokes equations, but I don't know how to do it in SLEPc.</div><div class=""> </div><div class="">29.10.2019, 12:05, "Dave May" <<a href="mailto:dave.mayhem23@gmail.com" class="">dave.mayhem23@gmail.com</a>>:</div><blockquote class=""><div class=""><div class=""> </div> <div class=""><div class="">On Tue, 29 Oct 2019 at 08:59, <<a href="mailto:av-baron@yandex.ru" class="">av-baron@yandex.ru</a>> wrote:</div><blockquote style="border-left-color:rgb( 204 , 204 , 204 );border-left-style:solid;border-left-width:1px;margin:0px 0px 0px 0.8ex;padding-left:1ex" class=""><div class="">Hi, Dave! Thank you for your assistance. The problem is that I don't have the matrix representation for my problem.</div></blockquote><div class=""> </div><div class="">You will have to explain in more detail if you want further help.</div><div class="">Explain what "I don't have the matrix representation for my problem" means.</div><div class="">If you don't have a matrix representation, how do you solve the forward problem??</div><div class=""> </div><div class="">Maybe you mean you use a matrix-free (MF) method. That is still a matrix representation of your problem, however the MF representation does not explicitly store the matrix a_{ij} entries in a CSR (or other) format.</div><div class=""> </div><blockquote style="border-left-color:rgb( 204 , 204 , 204 );border-left-style:solid;border-left-width:1px;margin:0px 0px 0px 0.8ex;padding-left:1ex" class=""><div class=""> I've searched <span style="background:#ffffff none 0% 0% repeat scroll;float:none;font:14px 'arial' , sans-serif;text-align:left;text-decoration-style:initial;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px" class=""><font color="#545454" class="">on the internet </font></span><span style="background:#ffffff none 0% 0% repeat scroll;color:#545454;float:none;font:400 14px 'arial' , sans-serif;text-align:left;text-decoration-style:initial;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px" class="">for a solution, but</span> found only some examples of solving 2D eigenvalue problems for the Stokes equations. Maybe you could help me with the matrix representation for the 3D Stokes eigenvalue problem?</div><div class="">Thank you in advance,</div><div class="">Alex</div><div class=""> </div><div class="">29.10.2019, 11:16, "Dave May" <<a href="mailto:dave.mayhem23@gmail.com" class="">dave.mayhem23@gmail.com</a>>:</div><blockquote class=""><div class=""> </div><div class=""> <div class=""><div class="">On Tue 29. Oct 2019 at 08:13, alex via petsc-users <<a href="mailto:petsc-users@mcs.anl.gov" class="">petsc-users@mcs.anl.gov</a>> wrote:</div><blockquote style="border-left-color:rgb( 204 , 204 , 204 );border-left-style:solid;border-left-width:1px;margin:0px 0px 0px 0.8ex;padding-left:1ex" class=""><div class=""><div class="">Hello!</div><div class="">In my project I have to calculate eigenvalues for the three dimensional Stokes equations with Dirichlet boundary conditions. I would like to use SLEPc iterative solver for this purpose, but I'm not quite sure how I should set up the matrices for the solver. I would be grateful if anyone could share a source code for solving this eigenvalue problem.</div></div></blockquote><div class=""> </div><div class="">I presume your forward model uses petsc. What matrix representation do you use in that code? Why cannot they be used directly with slepc?</div><div class=""> </div><div class="">Thanks</div><div class="">Dave</div><div class=""> </div><div class=""> </div><blockquote style="border-left-color:rgb( 204 , 204 , 204 );border-left-style:solid;border-left-width:1px;margin:0px 0px 0px 0.8ex;padding-left:1ex" class=""><div class=""><div class=""> </div><div class="">Thank you very much! </div></div><div class=""><div class="">Alex</div></div></blockquote></div></div></blockquote></blockquote></div></div></blockquote></div></blockquote></div><br class=""></div></body></html>