The four contributions to this volume are concerned, first with a family
of numerical methods of broad application but of particular interest in
electron imaging and second, with three ways of extracting information from
an image-forming instrument.
A superficial glance at any text on calculating field distributions will
reveal that, among the methods most frequently used are the finite-difference
and finite-element methods of transforming a differential equation into a
difference equation. To these must be added the finite-volume approach.
These methods are of course of immediate interest in numerous other areas
than the calculation of electric and magnetic field distributions and the
opening chapter, by C. Mattiussi, places this collection of methods in
context and brings out very clearly the family resemblance between them.