**``IE''**- 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.
**``CE''**- 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.
**``M,''**- 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 prescribed frequency.

Susan Blackford 2000-11-20