[petsc-users] Petsc has generated inconsistent data - Divide by zero!

Sat Jul 9 17:26:29 CDT 2011

2011/7/9 TAY wee-beng <zonexo at gmail.com>

> **
> Hi Jed,
>
> I have attached the output runing under linux. It's only running with 1
> processor. I am using runge kutta 3rd order to solve my problem, so there's
> 3 substeps per time step ie I need to solve the x/y momentum eqns 3 times
> per time step.
>

1) As Jed said, you have repeated output. Something is wrong with your MPI
setup. I suspect you are using
    the wrong mpiexec. Please do not send parallel results until your serial
results work.

2) Always run with -ksp_view when you send results

3) You did not try using LU as Jed suggested.

   Matt

> The error occurs at t=2, substep=2. It stated in the output.
>
> Btw, I am solving the x and y momentum eqns separately, since they are
> independent of one another. How can I solve it together?
>
> My code is:
>
> call MatSetValues(A_semi_x,1,II,1,JJ,semi_mat_x(k,kk),INSERT_VALUES,ierr)
> ...
>
> call MatAssemblyBegin(A_semi_x,MAT_FINAL_ASSEMBLY,ierr)
> call MatAssemblyEnd(A_semi_x,MAT_FINAL_ASSEMBLY,ierr)
>
> call KSPGetPC(ksp_semi_x,pc_semi_x,ierr)
> ksptype=KSPBCGS
> call KSPSetType(ksp_semi_x,ksptype,ierr)
> call KSPSetFromOptions(ksp_semi_x,ierr)
>
> tol=1.e-5
>
> call
> KSPSetTolerances(ksp_semi_x,tol,PETSC_DEFAULT_DOUBLE_PRECISION,PETSC_DEFAULT_DOUBLE_PRECISION,PETSC_DEFAULT_INTEGER,ierr)
>
> exactly the same for y...
>
> call VecAssemblyBegin(b_rhs_semi_x,ierr)
> call VecAssemblyEnd(b_rhs_semi_x,ierr)
>
> call VecAssemblyBegin(xx_semi_x,ierr)
> call VecAssemblyEnd(xx_semi_x,ierr)
>
> call
> KSPSetOperators(ksp_semi_x,A_semi_x,A_semi_x,SAME_NONZERO_PATTERN,ierr)
> call KSPSolve(ksp_semi_x,b_rhs_semi_x,xx_semi_x,ierr)
> call KSPGetConvergedReason(ksp_semi_x,reason,ierr)
>
> exactly the same for y...
>
> Thanks alot!
>
> Yours sincerely,
>
> TAY wee-beng
>
>
> On 9/7/2011 12:26 AM, Jed Brown wrote:
>
> On Fri, Jul 8, 2011 at 17:17, TAY wee-beng <zonexo at gmail.com> wrote:
>
>>  Hi Jed,
>>
>> This is my output when the error happens for gmres:
>>
>>   2 KSP preconditioned resid norm 1.556688898463e+007 true resid norm
>> 2.58995443
>> 8801e+003 ||Ae||/||Ax|| 1.232088736212e+003
>>   2 KSP preconditioned resid norm 1.556688898463e+007 true resid norm
>> 2.58995443
>> 8801e+003 ||Ae||/||Ax|| 1.232088736212e+003
>>   3 KSP preconditioned resid norm 1.207952812560e+003 true resid norm
>> 9.05939430
>> 1179e+003 ||Ae||/||Ax|| 4.309719703237e+003
>>   3 KSP preconditioned resid norm 1.207952812560e+003 true resid norm
>> 9.05939430
>> 1179e+003 ||Ae||/||Ax|| 4.309719703237e+003 3 KSP preconditioned resid
>> norm 1.207952812560e+003 true resid norm 9.05939430
>> 1179e+003 ||Ae||/||Ax|| 4.309719703237e+003
>>   3 KSP preconditioned resid norm 1.207952812560e+003 true resid norm
>> 9.05939430
>> 1179e+003 ||Ae||/||Ax|| 4.309719703237e+003
>>   3 KSP preconditioned resid norm 1.207952812560e+003 true resid norm
>> 9.05939430
>> 1179e+003 ||Ae||/||Ax|| 4.309719703237e+003
>>   4 KSP preconditioned resid norm 3.815055004710e+001 true resid norm
>> 1.96385966
>> 1729e+002 ||Ae||/||Ax|| 9.342439899591e+001
>>   4 KSP preconditioned resid norm 3.815055004710e+001 true resid norm
>> 1.96385966
>> 1729e+002 ||Ae||/||Ax|| 9.342439899591e+001
>>   4 KSP preconditioned resid norm 3.815055004710e+001 true resid norm
>> 1.96385966
>> 1729e+002 ||Ae||/||Ax|| 9.342439899591e+001
>>   4 KSP preconditioned resid norm 3.815055004710e+001 true resid norm
>> 1.96385966
>> 1729e+002 ||Ae||/||Ax|| 9.342439899591e+001
>>   4 KSP preconditioned resid norm 3.815055004710e+001 true resid norm
>> 1.96385966
>> 1729e+002 ||Ae||/||Ax|| 9.342439899591e+001
>>
>
>  Why is the same line output multiple times? Do you have an MPI problem?
>
>  This convergence looks funky; I suspect your preconditioner is singular
> and/or nonlinear. Please send -ksp_view output as you are running here and
> with -pc_type asm -sub_pc_type lu.
>
>
>>
>> for fgmres:
>>
>>  34 KSP preconditioned resid norm 2.428114102327e-005 true resid norm
>> 3.35941610
>> 6265e-005 ||Ae||/||Ax|| 1.598129588716e-005
>>  34 KSP preconditioned resid norm 2.428114102327e-005 true resid norm
>> 3.35941610
>> 6265e-005 ||Ae||/||Ax|| 1.598129588716e-005
>>  35 KSP preconditioned resid norm 2.200715659545e-005 true resid norm
>> 3.88294769
>> 5703e-005 ||Ae||/||Ax|| 1.847182191086e-005
>>  35 KSP preconditioned resid norm 2.200715659545e-005 true resid norm
>> 3.88294769
>> 5703e-005 ||Ae||/||Ax|| 1.847182191086e-005
>>  35 KSP preconditioned resid norm 2.200715659545e-005 true resid norm
>> 3.88294769
>> 5703e-005 ||Ae||/||Ax|| 1.847182191086e-005
>>  35 KSP preconditioned resid norm 2.200715659545e-005 true resid norm
>> 3.88294769
>> 5703e-005 ||Ae||/||Ax|| 1.847182191086e-005
>>  35 KSP preconditioned resid norm 2.200715659545e-005 true resid norm
>> 3.88294769
>> 5703e-005 ||Ae||/||Ax|| 1.847182191086e-005
>>  36 KSP preconditioned resid norm 2.011575409369e-005 true resid norm
>> 3.89282805
>> 6204e-005 ||Ae||/||Ax|| 1.851882441357e-005
>>  36 KSP preconditioned resid norm 2.011575409369e-005 true resid norm
>> 3.89282805
>> 6204e-005 ||Ae||/||Ax|| 1.851882441357e-005
>>  36 KSP preconditioned resid norm 2.011575409369e-005 true resid norm
>> 3.89282805
>> 6204e-005 ||Ae||/||Ax|| 1.851882441357e-005
>>  36 KSP preconditioned resid norm 2.011575409369e-005 true resid norm
>> 3.89282805
>> 6204e-005 ||Ae||/||Ax|| 1.851882441357e-005
>>  36 KSP preconditioned resid norm 2.011575409369e-005 true resid norm
>> 3.89282805
>> 6204e-005 ||Ae||/||Ax|| 1.851882441357e-005
>>
>> Btw, I am solving the x and y momentum eqns so there 's 2 eqns to solve.
>>
>
>  Do you solve them separately or both at once? (We usually recommend the
> latter.)
>
>
>

-- 
What most experimenters take for granted before they begin their experiments
is infinitely more interesting than any results to which their experiments
lead.
-- Norbert Wiener
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