<html><head><meta http-equiv="Content-Type" content="text/html charset=windows-1252"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;">Dear Jose,<div><br></div><div>Thanks for your prompt answer. Now I see the problem. </div><div>I will give it a try with "-st_matmode shell” first and see how it goes...</div><div><br></div><div><div>
<div>Kind regards,</div><div>Denis </div>
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<br><div><div>On 13 Oct 2014, at 19:27, Jose E. Roman <<a href="mailto:jroman@dsic.upv.es">jroman@dsic.upv.es</a>> wrote:</div><blockquote type="cite"><div style="font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><br>This case is discussed in section 3.4.2 of SLEPc's users guide. Basically, the default behaviour in shift-and-invert is that SLEPc builds matrix C=A-sigma*B (where sigma is the shift). In this case, the "A" matrix (the shell matrix in your case) needs two additional operations: duplicate and AXPY. You could implement these two operations in your shell matrix. You can also try with "-st_matmode inplace" in which case only AXPY is required. But probably what you want is to set "-st_matmode shell" so that you do not need any additional operation; the downside in all cases is that direct linear solves cannot be used and you must be cautious when using shift-and-invert with iterative linear solvers (see discussion at section 3.4.1).<br><br>Jose</div></blockquote></div><br></div></body></html>