<div>Hi,</div>
<div> </div>
<div>I've just tested with -ksp_type fgmres with rtol of 1.e-5 with 8 proceesors. It 's much better, although the last value still has some difference at .638e-2 and .635e-2. The original one was done with the default precon and solver.
</div>
<div> </div>
<div>Btw, if I use hypre as the precond then the value with 1 or 8 processors is the same.</div>
<div> </div>
<div>So am I right to say that the problem is due to the precon? What is the best way to ensure that my results are correct? </div>
<div> </div>
<div>I found that if I use the default precond and solver and did not use </div>
<div> </div>
<div>call KSPSetTolerances(ksp,tol,PETSC_DEFAULT_DOUBLE_PRECISION,PETSC_DEFAULT_DOUBLE_PRECISION,PETSC_DEFAULT_INTEGER,ierr)</div>
<div> </div>
<div>to set the tolerence to 1.e-8 when using 8 processors, I 'll get incorrect results. How can I avoid this?</div>
<div> </div>
<div>Thanks</div>
<div><br><br> </div>
<div><span class="gmail_quote">On 6/19/07, <b class="gmail_sendername">Barry Smith</b> <<a href="mailto:bsmith@mcs.anl.gov">bsmith@mcs.anl.gov</a>> wrote:</span>
<blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid"><br>Note that with 8 processors and a rtol of 1.e-5 the TRUE residual norm<br>is only 1.e-2 at the end while with one process it is
1.e-5. The<br>preconditioner is not working well with 8 processes, thought the<br>preconditioned residual norm is small the true residual norm is<br>not.<br><br> What KSP are you using? If gmres try using -ksp_type fgmres
<br>if cg try adding -ksp_norm_type unpreconditioned<br><br>Is the matrix symmetric? Do you expect/want it to be symmetric?<br><br> Barry<br><br><br>On Mon, 18 Jun 2007, Ben Tay wrote:<br><br>> Oh btw, here's the output when KSPSetTolerances =
1.0e-5.<br>><br>><br>> 1:<br>><br>> 0 KSP preconditioned resid norm 5.509130713952e+01 true resid norm<br>> 3.411770553001e+01 ||Ae||/||Ax|| 1.000000000000e+00<br>> 1 KSP preconditioned resid norm 6.561453237357e+00
true resid norm<br>> 8.697577384386e+00 ||Ae||/||Ax|| 2.549285554017e-01<br>> 2 KSP preconditioned resid norm 1.208347069756e+00 true resid norm<br>> 7.425376743449e+00 ||Ae||/||Ax|| 2.176399798315e-01<br>> 3 KSP preconditioned resid norm
3.386218089799e-01 true resid norm<br>> 7.347207820518e+00 ||Ae||/||Ax|| 2.153488256722e-01<br>> 4 KSP preconditioned resid norm 3.296482144730e-01 true resid norm<br>> 7.745880291985e+00 ||Ae||/||Ax|| 2.270340332579e-01
<br>> 5 KSP preconditioned resid norm 3.145738742595e-01 true resid norm<br>> 7.547707467510e+00 ||Ae||/||Ax|| 2.212255293918e-01<br>> 6 KSP preconditioned resid norm 1.643048266097e-01 true resid norm<br>>
4.306709238860e+00 ||Ae||/||Ax|| 1.262309165273e-01<br>> 7 KSP preconditioned resid norm 6.078974689223e-02 true resid norm<br>> 4.482652283996e+00 ||Ae||/||Ax|| 1.313878590122e-01<br>> 8 KSP preconditioned resid norm
6.054372794034e-02 true resid norm<br>> 4.355614139989e+00 ||Ae||/||Ax|| 1.276643335865e-01<br>> 9 KSP preconditioned resid norm 5.867972436189e-02 true resid norm<br>> 4.233715997285e+00 ||Ae||/||Ax|| 1.240914631132e-01
<br>> 10 KSP preconditioned resid norm 2.168073622951e-02 true resid norm<br>> 2.086394899960e+00 ||Ae||/||Ax|| 6.115284915993e-02<br>> 11 KSP preconditioned resid norm 1.139327427516e-02 true resid norm<br>>
2.155289979633e+00 ||Ae||/||Ax|| 6.317218424133e-02<br>> 12 KSP preconditioned resid norm 1.088027785149e-02 true resid norm<br>> 1.991898557592e+00 ||Ae||/||Ax|| 5.838313352696e-02<br>> 13 KSP preconditioned resid norm
1.072820075665e-02 true resid norm<br>> 1.942479796672e+00 ||Ae||/||Ax|| 5.693465508586e-02<br>> 14 KSP preconditioned resid norm 3.781319329677e-03 true resid norm<br>> 9.806622346091e-01 ||Ae||/||Ax|| 2.874349899487e-02
<br>> 15 KSP preconditioned resid norm 2.314101409645e-03 true resid norm<br>> 7.976384924484e-01 ||Ae||/||Ax|| 2.337901919420e-02<br>> 16 KSP preconditioned resid norm 2.293131061139e-03 true resid norm<br>>
7.897410852774e-01 ||Ae||/||Ax|| 2.314754386348e-02<br>> 17 KSP preconditioned resid norm 2.117223511336e-03 true resid norm<br>> 6.782416967980e-01 ||Ae||/||Ax|| 1.987946393996e-02<br>> 18 KSP preconditioned resid norm
7.524359734379e-05 true resid norm<br>> 9.092345849564e-04 ||Ae||/||Ax|| 2.664993354130e-05<br>><br>> 2:<br>><br>> 0 32<br>> 32 64<br>> 0 KSP preconditioned resid norm
4.902369798248e+01 true resid norm<br>> 3.411770553001e+01 ||Ae||/||Ax|| 1.000000000000e+00<br>> 1 KSP preconditioned resid norm 8.253504641663e+00 true resid norm<br>> 1.259698849910e+01 ||Ae||/||Ax|| 3.692214439222e-01
<br>> 2 KSP preconditioned resid norm 3.797891005886e+00 true resid norm<br>> 1.195333867118e+01 ||Ae||/||Ax|| 3.503558778495e-01<br>> 3 KSP preconditioned resid norm 2.578365901732e+00 true resid norm<br>>
1.159420670971e+01 ||Ae||/||Ax|| 3.398296142602e-01<br>> 4 KSP preconditioned resid norm 1.568196901288e+00 true resid norm<br>> 9.963750299049e+00 ||Ae||/||Ax|| 2.920404565390e-01<br>> 5 KSP preconditioned resid norm
1.317764005274e+00 true resid norm<br>> 9.066502566015e+00 ||Ae||/||Ax|| 2.657418611589e-01<br>> 6 KSP preconditioned resid norm 6.023727405584e-01 true resid norm<br>> 8.058099054033e+00 ||Ae||/||Ax|| 2.361852571517e-01
<br>> 7 KSP preconditioned resid norm 4.957651340342e-02 true resid norm<br>> 7.520037445249e+00 ||Ae||/||Ax|| 2.204145128879e-01<br>> 8 KSP preconditioned resid norm 2.449473557300e-02 true resid norm<br>>
7.475057378184e+00 ||Ae||/||Ax|| 2.190961338713e-01<br>> 9 KSP preconditioned resid norm 2.361338376271e-02 true resid norm<br>> 7.217194046579e+00 ||Ae||/||Ax|| 2.115380836566e-01<br>> 10 KSP preconditioned resid norm
2.307344735925e-02 true resid norm<br>> 7.205616297960e+00 ||Ae||/||Ax|| 2.111987364338e-01<br>> 11 KSP preconditioned resid norm 1.934171008299e-02 true resid norm<br>> 5.261866236257e+00 ||Ae||/||Ax|| 1.542268495057e-01
<br>> 12 KSP preconditioned resid norm 5.190847895073e-03 true resid norm<br>> 4.466349759791e+00 ||Ae||/||Ax|| 1.309100272251e-01<br>> 13 KSP preconditioned resid norm 4.871871781446e-03 true resid norm<br>>
4.194634080458e+00 ||Ae||/||Ax|| 1.229459606177e-01<br>> 14 KSP preconditioned resid norm 4.823921505423e-03 true resid norm<br>> 4.173223968428e+00 ||Ae||/||Ax|| 1.223184239268e-01<br>> 15 KSP preconditioned resid norm
4.701199647155e-03 true resid norm<br>> 3.957555688130e+00 ||Ae||/||Ax|| 1.159971230964e-01<br>> 16 KSP preconditioned resid norm 1.035300954721e-03 true resid norm<br>> 2.196668371922e+00 ||Ae||/||Ax|| 6.438499710918e-02
<br>> 17 KSP preconditioned resid norm 8.832653700092e-04 true resid norm<br>> 1.916576324421e+00 ||Ae||/||Ax|| 5.617541668313e-02<br>> 18 KSP preconditioned resid norm 8.703924311133e-04 true resid norm<br>>
1.916104922195e+00 ||Ae||/||Ax|| 5.616159974502e-02<br>> 19 KSP preconditioned resid norm 8.698960956884e-04 true resid norm<br>> 1.913670720373e+00 ||Ae||/||Ax|| 5.609025257250e-02<br>> 20 KSP preconditioned resid norm
3.690946760360e-04 true resid norm<br>> 7.994885772359e-01 ||Ae||/||Ax|| 2.343324572435e-02<br>><br>> 4:<br>><br>> 0 16<br>> 32 48<br>> 48 64<br>> 0 KSP preconditioned resid norm
4.414786383499e+01 true resid norm<br>> 3.411770553001e+01 ||Ae||/||Ax|| 1.000000000000e+00<br>> 1 KSP preconditioned resid norm 7.579678467669e+00 true resid norm<br>> 1.423835009315e+01 ||Ae||/||Ax|| 4.173302357811e-01
<br>> 2 KSP preconditioned resid norm 2.972753009220e+00 true resid norm<br>> 1.290812750005e+01 ||Ae||/||Ax|| 3.783410197001e-01<br>> 3 KSP preconditioned resid norm 1.347960602345e+00 true resid norm<br>>
1.173368275935e+01 ||Ae||/||Ax|| 3.439176983641e-01<br>> 4 KSP preconditioned resid norm 1.111052862809e+00 true resid norm<br>> 1.106221549565e+01 ||Ae||/||Ax|| 3.242367950541e-01<br>> 5 KSP preconditioned resid norm
9.872224937494e-01 true resid norm<br>> 1.005157038653e+01 ||Ae||/||Ax|| 2.946144891744e-01<br>> 6 KSP preconditioned resid norm 7.251219493841e-01 true resid norm<br>> 9.007852893929e+00 ||Ae||/||Ax|| 2.640228219921e-01
<br>> 7 KSP preconditioned resid norm 5.925185640664e-01 true resid norm<br>> 8.104036732737e+00 ||Ae||/||Ax|| 2.375317040476e-01<br>> 8 KSP preconditioned resid norm 3.381465672631e-01 true resid norm<br>>
7.256440004925e+00 ||Ae||/||Ax|| 2.126883942574e-01<br>> 9 KSP preconditioned resid norm 1.647154013552e-01 true resid norm<br>> 7.263797232535e+00 ||Ae||/||Ax|| 2.129040367661e-01<br>> 10 KSP preconditioned resid norm
7.697425793821e-02 true resid norm<br>> 7.155391777961e+00 ||Ae||/||Ax|| 2.097266409567e-01<br>> 11 KSP preconditioned resid norm 3.477770299629e-02 true resid norm<br>> 7.127853631055e+00 ||Ae||/||Ax|| 2.089194897583e-01
<br>> 12 KSP preconditioned resid norm 2.573627666614e-02 true resid norm<br>> 7.088156599392e+00 ||Ae||/||Ax|| 2.077559580657e-01<br>> 13 KSP preconditioned resid norm 2.221352319865e-02 true resid norm<br>>
7.093825972365e+00 ||Ae||/||Ax|| 2.079221290577e-01<br>> 14 KSP preconditioned resid norm 2.093106984691e-02 true resid norm<br>> 7.062268285770e+00 ||Ae||/||Ax|| 2.069971639669e-01<br>> 15 KSP preconditioned resid norm
2.034509930217e-02 true resid norm<br>> 7.031405865561e+00 ||Ae||/||Ax|| 2.060925773386e-01<br>> 16 KSP preconditioned resid norm 2.029393080560e-02 true resid norm<br>> 7.008984378537e+00 ||Ae||/||Ax|| 2.054353969487e-01
<br>> 17 KSP preconditioned resid norm 1.587358534265e-02 true resid norm<br>> 4.635842103718e+00 ||Ae||/||Ax|| 1.358778977572e-01<br>> 18 KSP preconditioned resid norm 1.055491860699e-02 true resid norm<br>>
3.773993858722e+00 ||Ae||/||Ax|| 1.106168718000e-01<br>> 19 KSP preconditioned resid norm 5.655638925006e-03 true resid norm<br>> 4.203919883144e+00 ||Ae||/||Ax|| 1.232181302299e-01<br>> 20 KSP preconditioned resid norm
4.767909232406e-03 true resid norm<br>> 4.121869307404e+00 ||Ae||/||Ax|| 1.208132036833e-01<br>> 21 KSP preconditioned resid norm 4.648572929978e-03 true resid norm<br>> 4.076834878296e+00 ||Ae||/||Ax|| 1.194932312992e-01
<br>> 22 KSP preconditioned resid norm 4.638216815872e-03 true resid norm<br>> 4.058874907114e+00 ||Ae||/||Ax|| 1.189668192529e-01<br>> 23 KSP preconditioned resid norm 1.851801714075e-03 true resid norm<br>>
2.017702443794e+00 ||Ae||/||Ax|| 5.913945303323e-02<br>> 24 KSP preconditioned resid norm 9.594251508173e-04 true resid norm<br>> 2.065135975225e+00 ||Ae||/||Ax|| 6.052974381317e-02<br>> 25 KSP preconditioned resid norm
8.609050236229e-04 true resid norm<br>> 1.901663497990e+00 ||Ae||/||Ax|| 5.573831734719e-02<br>> 26 KSP preconditioned resid norm 8.607029066323e-04 true resid norm<br>> 1.901221069645e+00 ||Ae||/||Ax|| 5.572534964205e-02
<br>> 27 KSP preconditioned resid norm 6.010429111401e-04 true resid norm<br>> 1.025962923033e+00 ||Ae||/||Ax|| 3.007127551793e-02<br>> 28 KSP preconditioned resid norm 2.036565987243e-04 true resid norm<br>>
8.385451121270e-01 ||Ae||/||Ax|| 2.457800426788e-02<br>><br>> 8:<br>><br>> 8 16<br>> 24 32<br>> 56 64<br>> 16 24<br>> 48 56
<br>> 0 8<br>> 32 40<br>> 40 48<br>> 0 KSP preconditioned resid norm 4.299803638671e+01 true resid norm<br>> 3.411770553001e+01 ||Ae||/||Ax|| 1.000000000000e+00
<br>> 1 KSP preconditioned resid norm 9.603727351867e+00 true resid norm<br>> 1.922897810349e+01 ||Ae||/||Ax|| 5.636070129797e-01<br>> 2 KSP preconditioned resid norm 2.931835632556e+00 true resid norm<br>>
1.355792423218e+01 ||Ae||/||Ax|| 3.973867533457e-01<br>> 3 KSP preconditioned resid norm 1.314351599619e+00 true resid norm<br>> 9.882281425137e+00 ||Ae||/||Ax|| 2.896525798443e-01<br>> 4 KSP preconditioned resid norm
8.218956530484e-01 true resid norm<br>> 9.318760482806e+00 ||Ae||/||Ax|| 2.731356150140e-01<br>> 5 KSP preconditioned resid norm 6.895693486764e-01 true resid norm<br>> 9.360126907217e+00 ||Ae||/||Ax|| 2.743480770998e-01
<br>> 6 KSP preconditioned resid norm 6.138748402770e-01 true resid norm<br>> 9.020243051395e+00 ||Ae||/||Ax|| 2.643859811575e-01<br>> 7 KSP preconditioned resid norm 5.265342569996e-01 true resid norm<br>>
8.781477094899e+00 ||Ae||/||Ax|| 2.573876806333e-01<br>> 8 KSP preconditioned resid norm 4.403325671754e-01 true resid norm<br>> 8.314776073768e+00 ||Ae||/||Ax|| 2.437085362160e-01<br>> 9 KSP preconditioned resid norm
2.353592633657e-01 true resid norm<br>> 7.347976506279e+00 ||Ae||/||Ax|| 2.153713560783e-01<br>> 10 KSP preconditioned resid norm 8.943808926292e-02 true resid norm<br>> 6.972332890712e+00 ||Ae||/||Ax|| 2.043611310432e-01
<br>> 11 KSP preconditioned resid norm 5.930469791557e-02 true resid norm<br>> 6.957386646797e+00 ||Ae||/||Ax|| 2.039230522310e-01<br>> 12 KSP preconditioned resid norm 5.283812047599e-02 true resid norm<br>>
6.981023245883e+00 ||Ae||/||Ax|| 2.046158479134e-01<br>> 13 KSP preconditioned resid norm 3.665176395384e-02 true resid norm<br>> 6.992078556546e+00 ||Ae||/||Ax|| 2.049398823258e-01<br>> 14 KSP preconditioned resid norm
2.516790937741e-02 true resid norm<br>> 6.949891196404e+00 ||Ae||/||Ax|| 2.037033583718e-01<br>> 15 KSP preconditioned resid norm 2.192690814272e-02 true resid norm<br>> 6.927621207906e+00 ||Ae||/||Ax|| 2.030506184483e-01
<br>> 16 KSP preconditioned resid norm 2.058802964863e-02 true resid norm<br>> 6.919125260713e+00 ||Ae||/||Ax|| 2.028015997332e-01<br>> 17 KSP preconditioned resid norm 1.984533974458e-02 true resid norm<br>>
6.853733693988e+00 ||Ae||/||Ax|| 2.008849536484e-01<br>> 18 KSP preconditioned resid norm 1.958243371255e-02 true resid norm<br>> 6.766030769290e+00 ||Ae||/||Ax|| 1.983143550887e-01<br>> 19 KSP preconditioned resid norm
1.874262002187e-02 true resid norm<br>> 6.323230908702e+00 ||Ae||/||Ax|| 1.853357607281e-01<br>> 20 KSP preconditioned resid norm 1.754461572091e-02 true resid norm<br>> 5.538708901675e+00 ||Ae||/||Ax|| 1.623411895857e-01
<br>> 21 KSP preconditioned resid norm 1.184321475064e-02 true resid norm<br>> 3.839931686898e+00 ||Ae||/||Ax|| 1.125495289688e-01<br>> 22 KSP preconditioned resid norm 1.070434172478e-02 true resid norm<br>>
3.754159266432e+00 ||Ae||/||Ax|| 1.100355140568e-01<br>> 23 KSP preconditioned resid norm 8.011880009497e-03 true resid norm<br>> 3.937870836170e+00 ||Ae||/||Ax|| 1.154201542864e-01<br>> 24 KSP preconditioned resid norm
5.573761552253e-03 true resid norm<br>> 4.205066407359e+00 ||Ae||/||Ax|| 1.232517351924e-01<br>> 25 KSP preconditioned resid norm 4.810675543540e-03 true resid norm<br>> 4.069723693466e+00 ||Ae||/||Ax|| 1.192848003769e-01
<br>> 26 KSP preconditioned resid norm 4.647944860704e-03 true resid norm<br>> 4.044329745280e+00 ||Ae||/||Ax|| 1.185404962746e-01<br>> 27 KSP preconditioned resid norm 4.606926939804e-03 true resid norm<br>>
4.039416044569e+00 ||Ae||/||Ax|| 1.183964742593e-01<br>> 28 KSP preconditioned resid norm 4.606174352197e-03 true resid norm<br>> 4.038658488893e+00 ||Ae||/||Ax|| 1.183742700792e-01<br>> 29 KSP preconditioned resid norm
4.604980580071e-03 true resid norm<br>> 4.034721549326e+00 ||Ae||/||Ax|| 1.182588772207e-01<br>> 30 KSP preconditioned resid norm 4.551931835395e-03 true resid norm<br>> 3.942692013899e+00 ||Ae||/||Ax|| 1.155614644259e-01
<br>> 31 KSP preconditioned resid norm 4.534435621643e-03 true resid norm<br>> 3.940744976447e+00 ||Ae||/||Ax|| 1.155043961846e-01<br>> 32 KSP preconditioned resid norm 4.533889403959e-03 true resid norm<br>>
3.940661031251e+00 ||Ae||/||Ax|| 1.155019357261e-01<br>> 33 KSP preconditioned resid norm 4.533315616020e-03 true resid norm<br>> 3.940962366962e+00 ||Ae||/||Ax|| 1.155107679646e-01<br>> 34 KSP preconditioned resid norm
4.533098107272e-03 true resid norm<br>> 3.940998854473e+00 ||Ae||/||Ax|| 1.155118374243e-01<br>> 35 KSP preconditioned resid norm 4.531113895054e-03 true resid norm<br>> 3.939900266217e+00 ||Ae||/||Ax|| 1.154796374789e-01
<br>> 36 KSP preconditioned resid norm 4.530789523555e-03 true resid norm<br>> 3.939483356865e+00 ||Ae||/||Ax|| 1.154674177430e-01<br>> 37 KSP preconditioned resid norm 4.530789514003e-03 true resid norm<br>>
3.939490762772e+00 ||Ae||/||Ax|| 1.154676348123e-01<br>> 38 KSP preconditioned resid norm 4.530624961751e-03 true resid norm<br>> 3.937889462104e+00 ||Ae||/||Ax|| 1.154207002179e-01<br>> 39 KSP preconditioned resid norm
4.517785703071e-03 true resid norm<br>> 3.927441577896e+00 ||Ae||/||Ax|| 1.151144696539e-01<br>> 40 KSP preconditioned resid norm 4.508890400648e-03 true resid norm<br>> 3.919421029911e+00 ||Ae||/||Ax|| 1.148793850297e-01
<br>> 41 KSP preconditioned resid norm 4.508823049754e-03 true resid norm<br>> 3.920408845458e+00 ||Ae||/||Ax|| 1.149083381943e-01<br>> 42 KSP preconditioned resid norm 4.504581641358e-03 true resid norm<br>>
3.910936323861e+00 ||Ae||/||Ax|| 1.146306957958e-01<br>> 43 KSP preconditioned resid norm 4.496299729031e-03 true resid norm<br>> 3.892573202489e+00 ||Ae||/||Ax|| 1.140924672987e-01<br>> 44 KSP preconditioned resid norm
4.327165698785e-03 true resid norm<br>> 3.499303379330e+00 ||Ae||/||Ax|| 1.025656129265e-01<br>> 45 KSP preconditioned resid norm 3.860049921599e-03 true resid norm<br>> 2.642394407576e+00 ||Ae||/||Ax|| 7.744935852298e-02
<br>> 46 KSP preconditioned resid norm 3.813681936798e-03 true resid norm<br>> 2.561643926848e+00 ||Ae||/||Ax|| 7.508253814415e-02<br>> 47 KSP preconditioned resid norm 3.811608329841e-03 true resid norm<br>>
2.553393452252e+00 ||Ae||/||Ax|| 7.484071430319e-02<br>> 48 KSP preconditioned resid norm 3.805700908518e-03 true resid norm<br>> 2.559614961583e+00 ||Ae||/||Ax|| 7.502306857451e-02<br>> 49 KSP preconditioned resid norm
3.783124026053e-03 true resid norm<br>> 2.523808739092e+00 ||Ae||/||Ax|| 7.397357764494e-02<br>> 50 KSP preconditioned resid norm 3.777662131381e-03 true resid norm<br>> 2.516105834856e+00 ||Ae||/||Ax|| 7.374780325255e-02
<br>> 51 KSP preconditioned resid norm 3.710923429451e-03 true resid norm<br>> 2.426657981798e+00 ||Ae||/||Ax|| 7.112606032852e-02<br>> 52 KSP preconditioned resid norm 3.604808013597e-03 true resid norm<br>>
2.303594181107e+00 ||Ae||/||Ax|| 6.751902407624e-02<br>> 53 KSP preconditioned resid norm 3.513880489788e-03 true resid norm<br>> 2.188212014004e+00 ||Ae||/||Ax|| 6.413713876742e-02<br>> 54 KSP preconditioned resid norm
3.320184202285e-03 true resid norm<br>> 1.978987642137e+00 ||Ae||/||Ax|| 5.800471079148e-02<br>> 55 KSP preconditioned resid norm 2.195662794099e-03 true resid norm<br>> 1.448538675887e+00 ||Ae||/||Ax|| 4.245709532291e-02
<br>> 56 KSP preconditioned resid norm 9.077826763324e-04 true resid norm<br>> 1.628573968470e+00 ||Ae||/||Ax|| 4.773398278607e-02<br>> 57 KSP preconditioned resid norm 7.602131391716e-04 true resid norm<br>>
1.659109675600e+00 ||Ae||/||Ax|| 4.862899335772e-02<br>> 58 KSP preconditioned resid norm 7.450227847936e-04 true resid norm<br>> 1.651479746174e+00 ||Ae||/||Ax|| 4.840535787852e-02<br>> 59 KSP preconditioned resid norm
7.410161195392e-04 true resid norm<br>> 1.649502155114e+00 ||Ae||/||Ax|| 4.834739410196e-02<br>> 60 KSP preconditioned resid norm 7.399447579004e-04 true resid norm<br>> 1.648188611058e+00 ||Ae||/||Ax|| 4.830889373871e-02
<br>> 61 KSP preconditioned resid norm 7.399146825366e-04 true resid norm<br>> 1.648156339888e+00 ||Ae||/||Ax|| 4.830794786121e-02<br>> 62 KSP preconditioned resid norm 7.399119217730e-04 true resid norm<br>>
1.648143662498e+00 ||Ae||/||Ax|| 4.830757628317e-02<br>> 63 KSP preconditioned resid norm 7.399115190929e-04 true resid norm<br>> 1.648149747433e+00 ||Ae||/||Ax|| 4.830775463441e-02<br>> 64 KSP preconditioned resid norm
7.398927702838e-04 true resid norm<br>> 1.648083443482e+00 ||Ae||/||Ax|| 4.830581124607e-02<br>> 65 KSP preconditioned resid norm 7.398398384099e-04 true resid norm<br>> 1.647873653551e+00 ||Ae||/||Ax|| 4.829966224141e-02
<br>> 66 KSP preconditioned resid norm 7.398251502315e-04 true resid norm<br>> 1.647783674785e+00 ||Ae||/||Ax|| 4.829702493725e-02<br>> 67 KSP preconditioned resid norm 7.398217631044e-04 true resid norm<br>>
1.647733028046e+00 ||Ae||/||Ax|| 4.829554046641e-02<br>> 68 KSP preconditioned resid norm 7.398045634717e-04 true resid norm<br>> 1.647630453201e+00 ||Ae||/||Ax|| 4.829253396748e-02<br>> 69 KSP preconditioned resid norm
7.397586859381e-04 true resid norm<br>> 1.647387302132e+00 ||Ae||/||Ax|| 4.828540713804e-02<br>> 70 KSP preconditioned resid norm 7.396782241138e-04 true resid norm<br>> 1.646889429724e+00 ||Ae||/||Ax|| 4.827081435109e-02
<br>> 71 KSP preconditioned resid norm 7.395189566969e-04 true resid norm<br>> 1.646041167917e+00 ||Ae||/||Ax|| 4.824595154763e-02<br>> 72 KSP preconditioned resid norm 7.391300711199e-04 true resid norm<br>>
1.643970513576e+00 ||Ae||/||Ax|| 4.818526005889e-02<br>> 73 KSP preconditioned resid norm 7.367639912300e-04 true resid norm<br>> 1.631221838831e+00 ||Ae||/||Ax|| 4.781159264642e-02<br>> 74 KSP preconditioned resid norm
7.075386327019e-04 true resid norm<br>> 1.473482203196e+00 ||Ae||/||Ax|| 4.318819745660e-02<br>> 75 KSP preconditioned resid norm 6.769663644505e-04 true resid norm<br>> 1.324870886213e+00 ||Ae||/||Ax|| 3.883235597562e-02
<br>> 76 KSP preconditioned resid norm 6.510062346881e-04 true resid norm<br>> 1.209103850108e+00 ||Ae||/||Ax|| 3.543919004296e-02<br>> 77 KSP preconditioned resid norm 6.416005299115e-04 true resid norm<br>>
1.174343461999e+00 ||Ae||/||Ax|| 3.442035282725e-02<br>> 78 KSP preconditioned resid norm 6.269785791288e-04 true resid norm<br>> 1.115598946804e+00 ||Ae||/||Ax|| 3.269853378102e-02<br>> 79 KSP preconditioned resid norm
6.143599514076e-04 true resid norm<br>> 1.060258719301e+00 ||Ae||/||Ax|| 3.107649540993e-02<br>> 80 KSP preconditioned resid norm 6.118239459355e-04 true resid norm<br>> 1.049506356947e+00 ||Ae||/||Ax|| 3.076134050174e-02
<br>> 81 KSP preconditioned resid norm 6.112876406857e-04 true resid norm<br>> 1.046662765401e+00 ||Ae||/||Ax|| 3.067799399581e-02<br>> 82 KSP preconditioned resid norm 6.092506607543e-04 true resid norm<br>>
1.042978389425e+00 ||Ae||/||Ax|| 3.057000385056e-02<br>> 83 KSP preconditioned resid norm 6.081618319409e-04 true resid norm<br>> 1.040456343908e+00 ||Ae||/||Ax|| 3.049608195349e-02<br>> 84 KSP preconditioned resid norm
6.071647595071e-04 true resid norm<br>> 1.037276486552e+00 ||Ae||/||Ax|| 3.040287939761e-02<br>> 85 KSP preconditioned resid norm 5.795095806265e-04 true resid norm<br>> 9.478301874350e-01 ||Ae||/||Ax|| 2.778118202003e-02
<br>> 86 KSP preconditioned resid norm 4.787555615154e-04 true resid norm<br>> 6.865840307207e-01 ||Ae||/||Ax|| 2.012398020485e-02<br>> 87 KSP preconditioned resid norm 4.213257765496e-04 true resid norm<br>>
5.905989111727e-01 ||Ae||/||Ax|| 1.731062807413e-02<br>><br>> It seems that the no. of lines is much lesser compared to the eariler case<br>> when KSPSetTolerances = 1.0e-8<br>><br>> Thanks again<br>><br>
><br>><br>> On 6/17/07, Barry Smith <<a href="mailto:bsmith@mcs.anl.gov">bsmith@mcs.anl.gov</a>> wrote:<br>> ><br>> ><br>> > Ben,<br>> ><br>> ><br>> > On Sat, 16 Jun 2007, Ben Tay wrote:
<br>> ><br>> > > Hi,<br>> > ><br>> > > I am trying to use PETSc to solve my poisson eqn. In the past, when I'm<br>> > not<br>> > > using MPI, I set KSPSetTolerances to 1.0e-5
. This seems to be good<br>> > enuff.<br>> > ><br>> > > Now, I'm trying to use PETSc with MPI to solve the eqn. I am using a<br>> > very<br>> > > small no. of pts, only 16x4. On 1 processor, the ans is the same as the
<br>> > one<br>> > > without MPI. However, on 2 processors, I found that I've to increase the<br>> > > KSPSetTolerances to 1.0e-6, else those grid pts on the edge will be<br>> > > different. On 4 processors, KSPSetTolerances has to be decreased to
<br>> > 1.0e-7.<br>> > > On 8 processors, when KSPSetTolerances is 1.0e-8, the difference of the<br>> > last<br>> > > pt between 1 and 8 processors is about 3%.<br>> > ><br>> >
<br>> > Are you using the same number of grid points when changing the number of<br>> > processors?<br>> ><br>> > Run the cases with -ksp_monitor_true_residual and send us ALL the<br>> > output.
<br>> ><br>> > Barry<br>> ><br>> ><br>> ><br>> > > May I know why this is so? Also, does this happens only on very small<br>> > grids?<br>> > > Does it happen on large grids as well? I usually solve grids with approx
<br>> > > 20000 to 55000 pts.<br>> > ><br>> > > Thank you.<br>> > ><br>> ><br>> ><br>><br><br></blockquote></div><br>