<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Matt<div><br></div><div>Thanks. Yes I can wait for a few weeks/months (its only a local memory footprint issue and in no way hampers my ability to solve problems).</div><div><br></div><div>Btw just for curiosity are you using the same technique discussed by Barry?</div><div><br></div><div>Maybe I am overlooking something trivial in his post.</div><div><br></div><div>Tabrez</div><div><br></div><div><br></div><div><div>On Jan 27, 2012, at 10:26 AM, Matthew Knepley wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite">On Fri, Jan 27, 2012 at 10:32 AM, Tabrez Ali <span dir="ltr"><<a href="mailto:stali@geology.wisc.edu">stali@geology.wisc.edu</a>></span> wrote:<br><div class="gmail_quote"><blockquote class="gmail_quote" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0.8ex; border-left-width: 1px; border-left-color: rgb(204, 204, 204); border-left-style: solid; padding-left: 1ex; position: static; z-index: auto; "> PETSc Gurus<br> <br> First I want to thank you for patiently answering questions that I have asked in past regarding preallocation. Unfortunately I am still having problems.<br> <br> I have a small unstructured FE (elasticity) code that uses PETSc.<br> <br> Unfortunately I am not yet able to find an _efficient_ way of calculating the non-zero structure so I simply overestimate the o_nz and d_nz values (= dimension x max_number_of nodes _a_node_contributes_to) which means that my stiffness matrix consumes at least 2X more memory. For example, for a perfectly structured mesh of linear hexes this number is 3*27=81=o_nz=d_nz. In complicated 3D linear tet/hex meshes that I have generated I rarely need to set a value greater than 150. In general I have found that as long as I keep DOF/core between 100-200K (assuming 1GB/per core) there is enough local RAM left even when memory for stiffness matrix is overestimated by 2X-6X.<br> <br> In any case now I do want to preallocate exactly for better memory performance and the ambiguity involved in choosing a reasonable o_nz/d_nz. The way I am trying to do it involves loops like ...<br> <br> do i=1, num_local_elements<br> do j=1, num_total_nodes<br> ...<br> end do<br> end do<br> <br> or using lists that involve searches.<br> <br> This unfortunately takes much time (much more than assembly and solve) due to the second loop. I am aware of many posts/slides by PETSc authors that mention that the non-zero structure can be found simply by looping once through elements but what to do next is not quite clear.<br> <br> I am also aware of this post by Barry [ <a href="http://lists.mcs.anl.gov/pipermail/petsc-users/2008-May/003020.html" target="_blank">http://lists.mcs.anl.gov/<u></u>pipermail/petsc-users/2008-<u></u>May/003020.html</a> ] but I cannot get it to work for a simple 4 element problem. Can some one please expand on the strategy being suggested by Barry specially where the loops are discussed (I understand the arrays and the vecscatter part). I am also not sure how does using a t of 0.5 and 1 prevents double counting. Shouldn't it be 0 and 1?<br> <br> I am also aware of some capabilities in DMMESH but right now I dont understand it well enough to utilize it.<br></blockquote><div><br></div><div>I agree with you here. Its not easy enough to use. However, I have rewritten the basics of it completely in C, which</div> <div>will all have easy Fortran bindings. You can specify your mesh with adjacency lists using Fortran arrays. The last part</div><div>I am working on is matrix preallocation. I would not normally ask you to wait, but I think I am pretty close. Mail me</div> <div>directly if you want more info. I think it should only take me a few weeks to finish.</div><div><br></div><div> Thanks,</div><div><br></div><div> Matt</div><div><br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"> Alternatively does PETSc support MATMPIAIJ of size=integer(1)/logical instead of real(8) which I can use to put zeros/ones (when I loop over elements the first time) to get the non-zero structure?<br> <br> Thanks in advance.<span class="HOEnZb"><font color="#888888"><br> <br> Tabrez<br> </font></span></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></blockquote></div><br></body></html>