<div class="gmail_extra">On Wed, Apr 25, 2012 at 1:42 PM, Dominik Szczerba <span dir="ltr"><<a href="mailto:dominik@itis.ethz.ch" target="_blank">dominik@itis.ethz.ch</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">
> Start by comparing residuals, with an without. Is SNES 0 the same? Is KSP 0<br>
> the same? KSP 1?<br>
<br>
BCGS, with the option:<br>
<br>
0 SNES Function norm 1.747536282885e+01<br>
0 KSP unpreconditioned resid norm 1.747536282885e+01 true resid norm<br>
1.747536282885e+01 ||r(i)||/||b|| 1.000000000000e+00<br>
1 KSP unpreconditioned resid norm 6.112827145626e-01 true resid norm<br>
1.751036369876e+01 ||r(i)||/||b|| 1.002002869425e+00<br>
<br>
BCGS, without:<br>
<br>
0 SNES Function norm 1.747536282885e+01<br>
0 KSP unpreconditioned resid norm 1.747536282885e+01 true resid norm<br>
1.747536282885e+01 ||r(i)||/||b|| 1.000000000000e+00<br>
1 KSP unpreconditioned resid norm 2.930616102426e-01 true resid norm<br>
2.930616102426e-01 ||r(i)||/||b|| 1.676998715922e-02<br>
<br>
GMRES, with the option:<br>
<br>
0 SNES Function norm 1.747536282885e+01<br>
0 KSP unpreconditioned resid norm 1.747536282885e+01 true resid norm<br>
1.747536282885e+01 ||r(i)||/||b|| 1.000000000000e+00<br>
1 KSP unpreconditioned resid norm 6.122286256494e-01 true resid norm<br>
1.747536251439e+01 ||r(i)||/||b|| 9.999999820055e-01<br></blockquote><div><br></div><div>Notice that there is no increase in the residual as is required. Notice also that</div><div>there is no decrease. This must mean that the preconditioner is rank deficient,</div>
<div>and I think it probably means that it is 0 since I find it hard to believe that P x</div><div>produces no component in the b direction.</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">
GMRES, without:<br>
<br>
0 SNES Function norm 1.747536282885e+01<br>
0 KSP unpreconditioned resid norm 1.747536282885e+01 true resid norm<br>
1.747536282885e+01 ||r(i)||/||b|| 1.000000000000e+00<br>
1 KSP unpreconditioned resid norm 6.122286294217e-01 true resid norm<br>
6.122286294218e-01 ||r(i)||/||b|| 3.503381505824e-02<br>
<span class="HOEnZb"><font color="#888888"><br>
Dominik<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>
</div>