<div class="gmail_quote">On Mon, Nov 8, 2010 at 12:36, Daniel Langr <span dir="ltr"><<a href="mailto:daniel.langr@gmail.com">daniel.langr@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
<div id=":44k">I am looking for several eigenvalues and eigenvectors with SLEPc.</div></blockquote><div><br></div><div>Presumably using methods that don't need a solve?</div><div><br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
<div id=":44k"><div class="im"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Where does the sparsity of the matrix come from?<br>
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Lie algebra, Slater determinants, SU(3) groups, new bases... But I don't understand all these things much, I just solve their (physicist's) eigenproblems.</div></blockquote><div><br></div><div>This more likely explains what the entries are, but not what the sparsity is. Sparse problems usually have some spatial locality (and/or locality in frequency or ensemble space). It is usually much easier to find a reasonable upper bound for the sparsity than to figure out exactly what the entries are. But I understand that this may be hard, such as if the support of the basis functions grew without bound due to some nonlinearity in the system.</div>
<div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;"><div id=":44k">I don't know the exact matrix structure, but I need some estimate about the number of nonzeros, since the matrix needs to fit into a memory. And I can simply use 85-90% of available memory for arrays, and just left some space for vectors (but vectors are very small - matrices are not much sparse). If I underestimate arrays' size, I will abort a computation, cause I don't have any more memory.</div>
</blockquote></div><br><div>Why not use MatMPISBAIJSetPreallocation and MatSetOption MAT_NEW_NONZERO_ALLOCATION_ERR to abort if you have underestimated? How would you do better than this yourself?</div><div><br></div><div>
Jed</div>