KSPSetTolerances and processors size
Ben Tay
zonexo at gmail.com
Mon Jun 18 22:14:29 CDT 2007
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?
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.
> > > >
> > >
> > >
> >
>
>
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