[petsc-users] Norm_2 calculation
Fazlul Huq
huq2090 at gmail.com
Fri Jun 5 14:08:29 CDT 2020
Thanks for the hint!
I will look at the matrix more closely.
For reference:
if (!rstart) {
rstart = 1;
i = 0; col[0] = 0; col[1] = 1; value[0] = 2.0; value[1] = -1.0;
ierr = MatSetValues(A,1,&i,2,col,value,INSERT_VALUES);CHKERRQ(ierr);
}
if (rend == n) {
rend = n-1;
i = n-1; col[0] = n-2; col[1] = n-1; value[0] = -1.0; value[1] = 2.0;
ierr = MatSetValues(A,1,&i,2,col,value,INSERT_VALUES);CHKERRQ(ierr);
}
/* Set entries corresponding to the mesh interior */
value[0] = -1.0; value[1] = 2.0; value[2] = -1.0;
for (i=rstart; i<rend; i++) {
col[0] = i-1; col[1] = i; col[2] = i+1;
ierr = MatSetValues(A,1,&i,3,col,value,INSERT_VALUES);CHKERRQ(ierr);
}
/* Assemble the matrix */
ierr = MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
ierr = MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
Sincerely,
Huq
On Fri, Jun 5, 2020 at 1:53 PM Matthew Knepley <knepley at gmail.com> wrote:
> On Fri, Jun 5, 2020 at 2:18 PM Fazlul Huq <huq2090 at gmail.com> wrote:
>
>> The same is happening with "-pc_type hypre -pc_hypre_type boomerang" and
>> with "-pc_type ilu".
>>
>> I tried with,
>> ierr =
>> KSPSetTolerances(ksp,1.e-10,PETSC_DEFAULT,PETSC_DEFAULT,PETSC_DEFAULT);CHKERRQ(ierr);
>> this also.
>>
>> Getting higher values of error even then.
>>
>
> Always check with
>
> -pc_type lu
>
> It seems likely that your matrix is flawed.
>
> Thanks,
>
> Matt
>
>
>> Any suggestion to go over this issue?
>> Shall I send the code? It's not a large script (single routine, less than
>> 100 lines except comment).
>>
>> Thank you.
>> Sincerely,
>> Huq
>>
>> On Fri, Jun 5, 2020 at 12:53 PM Matthew Knepley <knepley at gmail.com>
>> wrote:
>>
>>> On Fri, Jun 5, 2020 at 12:32 PM Fazlul Huq <huq2090 at gmail.com> wrote:
>>>
>>>> Input string:
>>>> mpiexec -np 1 ./poisson_m -n 10000000 -pc_type cholesky -ksp_view
>>>> -ksp_converged_reason -ksp_monitor_true_residual
>>>>
>>>> Output is attached herewith.
>>>>
>>>
>>> Solving the problem...
>>>
>>> 0 KSP preconditioned resid norm 9.741453255800e+07 true resid norm
>>> 1.802775638200e+01 ||r(i)||/||b|| 1.000000000000e+00
>>>
>>> 1 KSP preconditioned resid norm 5.796040438920e+00 true resid norm
>>> 3.146946078273e-05 ||r(i)||/||b|| 1.745611606675e-06
>>>
>>> Your Cholesky preconditioner is crap, probably because the system is
>>> either not symmetric or nearly singular. You can see this
>>> because the preconditioned residual is 6 orders of magnitude greater
>>> than the true residual. Also, if you want to evaluate convergence, you
>>> should probably use a lower tolerance like
>>>
>>> -ksp_rtol 1e-10
>>>
>>> Thanks,
>>>
>>> Matt
>>>
>>> Thank you.
>>>> Sincerely,
>>>> Huq
>>>>
>>>> On Fri, Jun 5, 2020 at 10:16 AM Matthew Knepley <knepley at gmail.com>
>>>> wrote:
>>>>
>>>>> On Fri, Jun 5, 2020 at 11:04 AM Fazlul Huq <huq2090 at gmail.com> wrote:
>>>>>
>>>>>> Hello All,
>>>>>> I'm trying to calculate the norm_2 error of a solution.
>>>>>> Here, vector s: Analytical solution
>>>>>> vector x: Numerical solution
>>>>>>
>>>>>> ierr = VecView(s,PETSC_VIEWER_STDOUT_WORLD);CHKERRQ(ierr);
>>>>>> ierr = VecView(x,PETSC_VIEWER_STDOUT_WORLD);CHKERRQ(ierr);
>>>>>>
>>>>>> ierr = VecAXPY(x,-1.0,s);CHKERRQ(ierr);
>>>>>> ierr = VecNorm(x,NORM_2,&norm);CHKERRQ(ierr);
>>>>>> ierr = VecView(x,PETSC_VIEWER_STDOUT_WORLD);CHKERRQ(ierr);
>>>>>> ierr = KSPGetIterationNumber(ksp,&its);CHKERRQ(ierr);
>>>>>> if (norm > tol) {
>>>>>> ierr = PetscPrintf(PETSC_COMM_WORLD,"Second Norm of error %g\n",
>>>>>> double)norm);CHKERRQ(ierr);
>>>>>> ierr = PetscPrintf(PETSC_COMM_WORLD,"Iterations
>>>>>> %D\n",its);CHKERRQ(ierr);
>>>>>> }
>>>>>>
>>>>>> Am I calculating the "Norm_2" error correctly or making any mistake?
>>>>>> Unfortunately, for large sized matrix, say 10^6, I am getting very
>>>>>> high value of "Norm_2" error.
>>>>>>
>>>>>
>>>>> 1) I am guessing x comes from a KSPSolve(). It is only as accurate as
>>>>> your tolerance
>>>>>
>>>>> 2) This is the l_2 norm, not the L_2 norm, so if you are using a
>>>>> continuum method like FEM, this is likely wrong.
>>>>>
>>>>> Thanks,
>>>>>
>>>>> Matt
>>>>>
>>>>>
>>>>>> Thank you.
>>>>>> Sincerely,
>>>>>> Huq
>>>>>>
>>>>>> --
>>>>>>
>>>>>> Fazlul Huq
>>>>>> Graduate Research Assistant
>>>>>> Department of Nuclear, Plasma & Radiological Engineering (NPRE)
>>>>>> University of Illinois at Urbana-Champaign (UIUC)
>>>>>> E-mail: huq2090 at gmail.com
>>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> 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
>>>>>
>>>>> https://www.cse.buffalo.edu/~knepley/
>>>>> <http://www.cse.buffalo.edu/~knepley/>
>>>>>
>>>>
>>>>
>>>> --
>>>>
>>>> Fazlul Huq
>>>> Graduate Research Assistant
>>>> Department of Nuclear, Plasma & Radiological Engineering (NPRE)
>>>> University of Illinois at Urbana-Champaign (UIUC)
>>>> E-mail: huq2090 at gmail.com
>>>>
>>>
>>>
>>> --
>>> 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
>>>
>>> https://www.cse.buffalo.edu/~knepley/
>>> <http://www.cse.buffalo.edu/~knepley/>
>>>
>>
>>
>> --
>>
>> Fazlul Huq
>> Graduate Research Assistant
>> Department of Nuclear, Plasma & Radiological Engineering (NPRE)
>> University of Illinois at Urbana-Champaign (UIUC)
>> E-mail: huq2090 at gmail.com
>>
>
>
> --
> 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
>
> https://www.cse.buffalo.edu/~knepley/
> <http://www.cse.buffalo.edu/~knepley/>
>
--
Fazlul Huq
Graduate Research Assistant
Department of Nuclear, Plasma & Radiological Engineering (NPRE)
University of Illinois at Urbana-Champaign (UIUC)
E-mail: huq2090 at gmail.com
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