finding some eigenvalues using eigs

I want to find eigenvalues of a matrix with size a few thoushands and I know the eigenvalues span through [- big number , + big number]. How can I find just those eigenvalues that they are in an specific range like: [-a , a] with a is known. Matrix is real symmetric. thanks

Answer 1

[David Sanchez]

I hope it helps:

greater_array = find( my_eigenvalue_array > -a );
wanted_eig_array = find (greater_array < a );