MATLAB Function Reference Volume 1: A - E - Bad Request

(lambda - 4.0), where lambda is an estimate of an eigenvalue of A.Aslambda
gets closer to 4.0, eigs fails. We must use sigma near but not equal to 4 to find
those 18 eigenvalues.
sigma = 4 - 1e-6
[V,D] = eigs(A,18,sigma)
The plot shows the 20 eigenvalues closest to 4 that were computed by eig,
along with the 18 eigenvalues closest to 4 - 1e-6 that were computed by eigs.
4.03
4.02
4.01
See Also arpackc, eig, svds
4
3.99
3.98
3.97
18 repeated eigenvalues of delsq(numgrid(’C’,30)) at 4
eigs(A,18,sigma)
eig(A)
2 4 6 8 10 12 14 16 18 20
References [1] Lehoucq, R.B. and D.C. Sorensen, “Deflation Techniques for an Implicitly
Re-Started Arnoldi Iteration,” SIAM J. Matrix Analysis and Applications, Vol.
17, 1996, pp. 789-821.
[2] Lehoucq, R.B., D.C. Sorensen, and C. Yang, ARPACK Users' Guide:
Solution of Large-Scale Eigenvalue Problems with Implicitly Restarted Arnoldi
Methods, SIAM Publications, Philadelphia, 1998.
eigs
2-479