[petsc-users] slepc eigenvectors

[Dharmendar Reddy]

I use EPS_GHEP and PetscScalar is complex. I am wondering why i see this
result.
You can see from the eigenvectors in the previous email that the magnitudes
of the components match. For the lapack/matlab solution the phase is pi
(180 degres)  for each component where as for defualt or arpack method
phase is 56.53 degrees for each component. I will prepare a test case and
email the code.

thanks
Reddy

On Tue, Jan 3, 2012 at 1:59 AM, Jose E. Roman <jroman at dsic.upv.es> wrote:

>
> On 03/01/2012, Dharmendar Reddy wrote:
>
> > Hello,
> >          I have a query regarding the eigenvectors computed in slepc. I
> am solving a genralized eigenvalue problem. I have attached the A and B
> matrices with this email.  If i run slepc solver with default options are
> arpack, i get one set of vectors (complex) as solution. If i run with
> eps_type lapack I get real vectors. A is hermitian, and B is positive
> definite. ( the actual problem is a schrodinger equation for particle in
> infinite potential well, so the solution will be of the form sin(x)). I
> check the solution in matlab using eig(A,B) i get real vectors. Looks like
> there is some unitary transformation involved here, can you tell me what
> could be going on.
> >
> > i copy a small portion of the eigen vector of the lowest magnitude
> eigenvlaue (=0.0887)
> > ---Method: (slepc and eps_type lapack) or matlab-----
> > (-0.101596582735892,0.000000000000000E+000)
> >  (-0.200421875537261,0.000000000000000E+000)
> >  (-0.293780182034781,0.000000000000000E+000)
> >  (-0.379124930994127,0.000000000000000E+000)
> >  ...
> >  ...
> >  ...
> >   (-0.293780182033444,0.000000000000000E+000)
> >  (-0.200421875536298,0.000000000000000E+000)
> >  (-0.101596582735387,0.000000000000000E+000)
> >
> ------------------------------------------------------------------------------
> > ---Method: (slepc and eps_type defualt or arpack) ----
> >
> >
> >   (5.602609025416389E-002,8.475224384072830E-002)
> >  (0.110523934800485,0.167192667375096)
> (0.162006974547097,0.245072510835553)
> >  (0.209070886310831,0.316267414979582)
> (0.250431889351034,0.378835368586700)
> >  (0.284961763219882,0.431069680779720)
> (0.311718623092706,0.471545535910556)
> >  (0.329972611445050,0.499158857936955)
> (0.339225807211469,0.513156427631836)
> >  (0.339225807166595,0.513156427588630)
> (0.329972611486755,0.499158857980068)
> >  (0.311718623054404,0.471545535864886)
> (0.284961763251251,0.431069680822535)
> >  (0.250431889322221,0.378835368543795)
> (0.209070886332945,0.316267415014661)
> >  (0.162006974528570,0.245072510805346)
> (0.110523934811968,0.167192667394530)
> >  (5.602609024797538E-002,8.475224382992022E-002)
>
> I cannot reproduce the problem. I always get the correct eigenvector. Are
> you doing the computation in real arithmetic? Are you setting the problem
> type to EPS_GHEP?
>
> Jose
>
>
>
>


-- 
-----------------------------------------------------
Dharmendar Reddy Palle
Graduate Student
Microelectronics Research center,
University of Texas at Austin,
10100 Burnet Road, Bldg. 160
MER 2.608F, TX 78758-4445
e-mail: dharmareddy84 at gmail.com
Phone: +1-512-350-9082
United States of America.
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