[petsc-users] SLEPc generalized eigenvalue problem question?

[John Chludzinski]

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.

---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
>>
>
>
>
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