On Sat, Oct 1, 2011 at 10:44 AM, behzad baghapour <span dir="ltr"><<a href="mailto:behzad.baghapour@gmail.com">behzad.baghapour@gmail.com</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;">
<div>OK. All I am concering is:</div>
<div> </div>
<div>1- define matrix A in sparse format AIJ.</div>
<div>2- Get the content of A.</div>
<div>3- change the content of A for some elements</div>
<div>4- Restore the changed matrix back into origin.</div>
<div> </div>
<div>I test MatGetArray( Mat A, PetscScalar* a ) but I couldnt find the correct content of matrix by using a[i*n+j]. I need to know how to access the elements of an assembled sparse matrix.<br><br></div>
<div>Am I clear now?</div></blockquote><div><br></div><div>No, definitely do not do that. The whole point of PETSc matrices is that you do not do this. This is what</div><div>is wrong with 90% of numerical software. You want <b>interfaces</b>, not data structures. That allows you</div>
<div>to seamlessly</div><div><br></div><div> - work in parallel</div><div> - work on GPUs</div><div> - optimize for different architectures</div><div><br></div><div>What you want to do is use MatSetValues() (or MatZeroRows, etc.) to change your entries.</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;"><div> </div>
<div>Thanks</div>
<div>Behzad</div>
<div> </div>
<div class="gmail_quote">On Sat, Oct 1, 2011 at 6:56 PM, Jed Brown <span dir="ltr"><<a href="mailto:jedbrown@mcs.anl.gov" target="_blank">jedbrown@mcs.anl.gov</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="padding-left:1ex;margin:0px 0px 0px 0.8ex;border-left:#ccc 1px solid">
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<div>On Sat, Oct 1, 2011 at 10:23, behzad baghapour <span dir="ltr"><<a href="mailto:behzad.baghapour@gmail.com" target="_blank">behzad.baghapour@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="padding-left:1ex;margin:0px 0px 0px 0.8ex;border-left:#ccc 1px solid">I meant by MatAssembly, the global indices of matrix elements (related to a dense format) which is changed into sparse one.</blockquote>
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<div>I don't understand what you mean. It doesn't make sense to convert "dense" indices into sparse ones.</div>
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<blockquote class="gmail_quote" style="padding-left:1ex;margin:0px 0px 0px 0.8ex;border-left:#ccc 1px solid">So what would be right pattern to read the content of the Matrix from MatGetArray if I know that the original matrix is created by AIJ?</blockquote>
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<div>Use MatGetRow() if you need access to this. (The internal data structures are different in parallel and serial, so accessing them directly is bad.)</div></blockquote></div><br><font color="#888888"><br clear="all"><br>
-- <br>==================================<br>
Behzad Baghapour<br>Ph.D. Candidate, Mechecanical Engineering<br>University of Tehran, Tehran, Iran<br><a href="https://sites.google.com/site/behzadbaghapour" target="_blank">https://sites.google.com/site/behzadbaghapour</a><br>
Fax: 0098-21-88020741<br>==================================<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>