Why do I receive an error when I use the EIGS function in MATLAB 7.0 (R14)?

I use the following code to load a sparse matrix and determine its eigenvalue with the largest real part:

load matlabmat;

eigs(O, 1, 'lr');

However, I receive the following error:

 ??? Error using ==> eigs>processEUPDinfo

 Error with ARPACK routine dneupd:

 dnaupd did not find any eigenvalues to sufficient accuracy.

 Error in ==> eigs at 369

 flag = processEUPDinfo(nargin<3);

Answer 1

[MathWorks Support Team]

This error occurs when the input matrix of the EIGS function has a very high condition number, which makes EIGS unable to converge to the default tolerance of EPS.

As a workaround, reduce the tolerance of EIGS using the following commands:

opts.tol = 1e-3; 

eigs(O, 1, 'lr', opts);