**``IE''**- stands for one or a few isolated eigenvalues at the end of the spectrum.
**``CE''**- stands for one or several eigenvalues at the end of the spectrum, possibly clustered, a typical example being computing the lowest eigenmodes of a vibrating mechanical system, modeled by finite element methods.
**``M''**- means some eigenvalues in the middle of the spectrum, most often in a specified interval, such as seeking all eigenmodes of a mechanical or electrical system excited by an external load of a prescribed frequency.

Susan Blackford 2000-11-20