[petsc-users] SLEPc generalized eigenvalue problem question?

[Matthew Knepley]

On Mon, Aug 1, 2011 at 6:22 PM, John Chludzinski <jchludzinski at gmail.com>wrote:

> I'm a newbie with both PETSc & SLEPc and have had some trouble finding
> examples/tutorials for newbies.  I've looked through the examples in the
> PETSc and SLEPc directories but still am having "issues" seeing how to set
> this up for the type of problem I have.
>
> SLEPc ex7.c is a good place to start but there's still how best to store
> the matrices and which EPS to use (besides LAPACK).
>
> Found a PDF, "MATRICES IN PETSc", (after much googling) but not sure which
> of the many forms will work and which is best.
>

1) PETSc and SLEPc are designed to be efficient for sparse matrices. If you
want eigenvalues of dense matrices, use Elemental (as I pointed out in a
previous message)

2) If you generate matrices with C code, why not just call MatSetValues()
for each row in that code?

   Matt


> ---John
>
>
> On Mon, Aug 1, 2011 at 2:12 PM, John Chludzinski <jchludzinski at gmail.com>wrote:
>
>> I have 2 files (matrices) in simply binary form (IEEE-754, generated by
>> some C code) and wished to get them into canonical "PETSc binary form". So I
>> did:
>>
>> Mat A;
>> PetscScalar *a;
>>
>> ierr = PetscMalloc(SIZE*SIZE*sizeof(PetscScalar),&a);CHKERRQ(ierr);
>> // stored the file into the space malloc'ed for 'a'.
>> MatCreateSeqDense(PETSC_COMM_SELF, n, n, a, &A);
>> MatView(A,PETSC_VIEWER_BINARY_(PETSC_COMM_WORLD));
>>
>> This works when I use: -eps_type lapack.  As long as I store the matrix in
>> column major order.
>>
>> ---John
>>
>> On Mon, Aug 1, 2011 at 1:40 PM, Matthew Knepley <knepley at gmail.com>wrote:
>>
>> On Mon, Aug 1, 2011 at 5:27 PM, John Chludzinski <jchludzinski at gmail.com>wrote:
>>>
>>>> I create 2 matrices using:
>>>>
>>>> MatCreateSeqDense(PETSC_COMM_SELF, n, n, Ka, &A);
>>>> MatCreateSeqDense(PETSC_COMM_SELF, n, n, Kb, &B);
>>>>
>>>> These matrices are 99% zeros ( 16,016,004 entries and 18660 non-zeros).
>>>>  They are symmetric and real.  Their tri-diagonal elements are non-zero plus
>>>> a few other entries.
>>>>
>>>
>>> Please give some justification for doing this? On the surface, it just
>>> seems perverse.
>>>
>>>    Matt
>>>
>>>
>>>> I tried to use ex7 for the generalized eigenvalue problem:
>>>>
>>>> ./ex7.exe -f1 k.dat -f2 m.dat -eps_gen_hermitian -eps_smallest_real >
>>>> x.out 2>&1
>>>>
>>>> without specifying an EPS and get:
>>>>
>>>> Generalized eigenproblem stored in file.
>>>>
>>>> Reading REAL matrices from binary files...
>>>> Number of iterations of the method: 500
>>>>  Number of linear iterations of the method: 4009
>>>> Solution method: krylovschur
>>>>
>>>> Number of requested eigenvalues: 1
>>>> Stopping condition: tol=1e-07, maxit=500
>>>> Number of converged approximate eigenpairs: 0
>>>>
>>>> Is krylovschur inappropriate for this problem or have I set up the
>>>> problem incorrectly by using   MatCreateSeqDense(...) to create the matrix
>>>> input files in PETSc binary form?
>>>>
>>>> ---John
>>>>
>>>
>>>
>>> --
>>> 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
>>>
>>
>>
>>
>


-- 
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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