<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">OK, I've tested ex56 with <div><br></div><div>-mg_levels_ksp_chebychev_estimate_eigenvalues 0,0.1,0,1.1</div><div><br></div><div>and verified that it does indeed overwrite my eigen estimates, that I give it, and I see very similar results (ie, with and w/o this est parameter). For instance with Cheb 1:</div><div><br></div><div><div> 0 KSP Residual norm 3.095373678236e+03 </div><div> 1 KSP Residual norm 6.191349513594e+02 </div><div> 2 KSP Residual norm 2.757450827269e+02 </div><div> 3 KSP Residual norm 1.268581869233e+02 </div><div> 4 KSP Residual norm 4.464752378561e+01 </div><div> 5 KSP Residual norm 1.695065935428e+01 </div><div> 6 KSP Residual norm 6.815970347827e+00 </div><div> 7 KSP Residual norm 2.924716764895e+00 </div><div> 8 KSP Residual norm 1.540893486351e+00 </div><div> 9 KSP Residual norm 6.455120265352e-01 </div><div> 10 KSP Residual norm 1.674033387830e-01 </div><div> 11 KSP Residual norm 5.847190034854e-02 </div><div> 12 KSP Residual norm 1.815782398062e-02 </div><div> 13 KSP Residual norm 5.013740651171e-03 </div><div> 14 KSP Residual norm 1.548353609674e-03 </div><div> 15 KSP Residual norm 4.575592583815e-04 </div><div> 16 KSP Residual norm 1.282184254689e-04 </div><div> 17 KSP Residual norm 3.708048113061e-05 </div><div> 18 KSP Residual norm 1.028830485881e-05 </div><div> 19 KSP Residual norm 2.695204689566e-06 </div><div> 20 KSP Residual norm 9.427412676529e-07 </div><div> 21 KSP Residual norm 2.719376922239e-07 </div><div>#PETSc Option Table entries:</div><div>-ksp_type cg</div><div>-mg_levels_ksp_chebychev_estimate_eigenvalues 0,0.1,0,1.1</div><div>-mg_levels_ksp_max_it 1</div></div><div><br></div><div>and Cheb-4:</div><div><br></div><div><div> 0 KSP Residual norm 3.273154874986e+03 </div><div> 1 KSP Residual norm 8.622241525141e+02 </div><div> 2 KSP Residual norm 4.096563608952e+02 </div><div> 3 KSP Residual norm 1.092011557684e+02 </div><div> 4 KSP Residual norm 2.723342496813e+01 </div><div> 5 KSP Residual norm 1.091986699964e+01 </div><div> 6 KSP Residual norm 5.433492162060e+00 </div><div> 7 KSP Residual norm 2.629892421938e+00 </div><div> 8 KSP Residual norm 5.300747644771e-01 </div><div> 9 KSP Residual norm 7.312379355566e-02 </div><div> 10 KSP Residual norm 2.279979060480e-02 </div><div> 11 KSP Residual norm 5.098259681590e-03 </div><div> 12 KSP Residual norm 1.468248636922e-03 </div><div> 13 KSP Residual norm 3.480984243626e-04 </div><div> 14 KSP Residual norm 7.966349284530e-05 </div><div> 15 KSP Residual norm 1.371697533223e-05 </div><div> 16 KSP Residual norm 3.107050969110e-06 </div><div> 17 KSP Residual norm 9.351516917154e-07 </div><div> 18 KSP Residual norm 2.555571755850e-07 </div><div>#PETSc Option Table entries:</div><div>-ksp_type cg</div><div>-mg_levels_ksp_chebychev_estimate_eigenvalues 0,0.1,0,1.1</div><div>-mg_levels_ksp_max_it 4</div></div><div><br></div><div>So I don't see anything wrong ... maybe this is just the way it is or there is a problem in the test, or algorithm/implementation.</div><div><br></div><div>Oh well, something to think about.</div><div><br></div><div>Mark</div><div><br><div><div>On Dec 26, 2011, at 10:27 PM, Jed Brown wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div class="gmail_quote">On Mon, Dec 26, 2011 at 12:43, Mark F. Adams <span dir="ltr"><<a href="mailto:mark.adams@columbia.edu">mark.adams@columbia.edu</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
I've just started using -ksp_rtol 1.e-10 and retested all of these test and am seeing a very slight improvement going from 1 to 4. I would expect to see a significant drop, say 25%, in the number of iterations going from 1 to 2. The < 5% that I am seeing seems too low but I'm not 100% sure -- maybe there is nothing wrong ...</blockquote>
</div><br><div>Well, here is a different test, just for giggles. This sets up rapid coarsening so that multigrid convergence with weak smoothers isn't already "too good".</div><div><br></div><div><div>$ pwd</div>
<div>/home/jed/petsc/src/snes/examples/tutorials</div></div><div><div>$ for n in {1..4}; do echo Cheby $n; ./ex5 -da_grid_x 5 -da_grid_y 5 -da_refine 3 -da_refine_x 4 -da_refine_y 4 -snes_max_it 1 -ksp_monitor -pc_type mg -pc_mg_levels 4 -mg_levels_pc_type jacobi -mg_levels_ksp_type chebychev -mg_levels_ksp_chebychev_estimate_eigenvalues 0,0.1,0,1.1 -mg_levels_ksp_max_it $n; done</div>
<div>Cheby 1</div><div> 0 KSP Residual norm 1.621385151256e+01 </div><div> 1 KSP Residual norm 1.247824515555e+01 </div><div> 2 KSP Residual norm 1.278794763626e+00 </div><div> 3 KSP Residual norm 1.116456717457e-01 </div>
<div> 4 KSP Residual norm 4.348273343707e-02 </div><div> 5 KSP Residual norm 8.348548286503e-03 </div><div> 6 KSP Residual norm 3.951234403814e-03 </div><div> 7 KSP Residual norm 1.058691144871e-03 </div><div>
8 KSP Residual norm 3.264344380115e-04 </div><div> 9 KSP Residual norm 8.173798438913e-05 </div><div>Cheby 2</div><div> 0 KSP Residual norm 1.891099688325e+01 </div><div> 1 KSP Residual norm 9.980070235568e+00 </div>
<div> 2 KSP Residual norm 8.251956879061e-02 </div><div> 3 KSP Residual norm 8.973973844623e-03 </div><div> 4 KSP Residual norm 6.086189552261e-04 </div><div> 5 KSP Residual norm 8.406518096327e-05 </div><div>
Cheby 3</div><div> 0 KSP Residual norm 1.990124921919e+01 </div><div> 1 KSP Residual norm 1.111981517647e+01 </div><div> 2 KSP Residual norm 4.888111472342e-02 </div><div> 3 KSP Residual norm 2.109153682849e-03 </div>
<div> 4 KSP Residual norm 1.680361259338e-04 </div><div>Cheby 4</div><div> 0 KSP Residual norm 2.051550954711e+01 </div><div> 1 KSP Residual norm 1.049577156306e+01 </div><div> 2 KSP Residual norm 3.445878799134e-02 </div>
<div> 3 KSP Residual norm 9.302079492533e-04 </div><div> 4 KSP Residual norm 3.995254526577e-05 </div><div><br></div></div><div><br></div><div>I don't think the Cheby implementation is buggy and I think we are using it correctly. I agree that it is somewhat disappointing if increasing the order above 1 doesn't make a more noticeable improvement.</div>
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