We give three typical cases:
- stands for one or a few isolated eigenvalues at the end of
the spectrum. This is the simplest case, a typical example being
the computation of a few leading singular values of a data matrix.
- stands for one or several eigenvalues at the end of the
spectrum, possibly clustered, a typical example being the computation of
the lowest eigenmodes of a vibrating mechanical system,
modeled by the finite element method.
- finally, means some eigenvalues in the middle of the spectrum,
most often in a specified interval, like seeking all eigenmodes of a
mechanical or electrical system excited by an external load of a