Field mapping using a computer: simple procedure across matching boundary

In field mapping, it may be necessary to carry out the computation across a matching boundary. The paper describes an improved and simple procedure for setting up the relevant equations near such a boundary, using the concept of `virtual nodes¿ in preference to that of `joined networks¿. Considerable improvement in accuracy results from the virtual-node method, as is revealed by tests on standard problems. Errors of even lesser magnitude, however, still remain, and their causes are investigated in a companion paper (see pages 330¿332).