[SciPy-user] generalized eigenvalue problem for sparse matrices
Neilen Marais
nmarais@sun.ac...
Tue Apr 15 07:54:35 CDT 2008
Abinav,
On Tue, 15 Apr 2008 01:50:20 +0530, abhinav sarkar wrote:
> Hi
> n = 3
> h = 1.0/(n+1)
>
> a = 1
> Pr = 7.0
> Ra = 1000
>
> A = get_A_mat(n, h, a, Pr, Ra)
> M = get_M_mat(n, h, a, Pr, Ra)
>
> sigma = 10.0
^^^
I think you're looking for -10.
> B = A - sigma*M
> s = dsolve.splu(B)
> e, v = ARPACK_gen_eigs(M.matvec, s.solve, 2*n, sigma, 2, 'LR')
^^
You may try futzing around with this parameter.
Anyway, I did play around a bit with your example and never really got a
good answer. But my experience has been that ARPACK doesn't really work
well with small matrices. Try a bigger problem and see if things turn out
better, I mean, obviously you don't need a sparse solver to solve a 6x6
matrix system ;). You may also find that if you force Matlab to do this
problem using a sparse solver you'll run into the same issues.
Unfortunately I don't know enough about the ARPACK routines to give more
insight. They do work quite well on my problems, where the eigenvalues
are always positive.
> which also seems to be correct to me. Please tell if the method I am
> using is correct or not and why am I not getting correct solutions. Is
> the ARPACK_gen_eigs broken? Or is there a problem in my code?
Seems OK, but I'm no expert ;)
Regards
Neilen
>
> Regards
> --
> Abhinav Sarkar
> 4th year Undergraduate Student
> Deptt. of Mechanical Engg.
> Indian Institute of Technology, Kharagpur India
>
> Web: http://claimid.com/abhin4v
> Twitter: http://twitter.com/abhin4v
> ---------
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