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