On Tue, Dec 2, 2008 at 7:52 PM, Chris Cooper <span dir="ltr"><<a href="mailto:chrisc@al.com.au">chrisc@al.com.au</a>></span> wrote:<br><div class="gmail_quote"><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
Hi,<br>
<br>
Just wondering if there are any techniques for improving DMMG convergence on a linear problem when operating in single precision?<br>
<br>
eg using ksp example 34 in Petsc 2.3.3 with multigrid levels changed to 6...<br>
<br>
double precision:<br>
0 KSP Residual norm 4.451733404502e-02<br>
1 KSP Residual norm 2.801676364873e-04<br>
2 KSP Residual norm 3.215426166316e-06<br>
3 KSP Residual norm 5.446277176355e-08<br>
Residual norm 5.44628e-08<br>
Error norm 0.000356798<br>
Error norm 9.21724e-05<br>
Error norm 1.34208e-07<br>
<br>
single precision:<br>
0 KSP Residual norm 4.450287297368e-02<br>
1 KSP Residual norm 2.799208450597e-04<br>
2 KSP Residual norm 2.232483529951e-05<br>
3 KSP Residual norm 1.575733222126e-05<br>
4 KSP Residual norm 1.286925271415e-05<br>
...<br>
27 KSP Residual norm 4.369261660031e-06<br>
28 KSP Residual norm 4.287577212381e-06<br>
29 KSP Residual norm 4.210308816255e-06<br>
30 KSP Residual norm 2.235170904896e-05<br>
31 KSP Residual norm 1.709007477757e-07</blockquote><div> <br>This bothers me. Shouldn't the Residual norm be the same as the last<br>residual, as it is above?<br><br> Matt<br><br></div><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
Residual norm 8.45584e-07<br>
Error norm 0.000370784<br>
Error norm 9.54664e-05<br>
Error norm 1.38935e-07<br>
<br>
thanks,<br>
Chris Cooper<br>
Animal Logic<br>
<br>
Animal Logic<br>
<a href="http://www.animallogic.com" target="_blank">http://www.animallogic.com</a><br>
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</blockquote></div><br><br clear="all"><br>-- <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>