In the context of this paper, regression means the evaluation of any effects generated in unmodified parts of a program by modifications in other parts. This is particularly important when complex and bloated software is upgraded.

Most industrial testing is done via test suites, that is, sets of procedures designed to exercise all parts of a program and to show up computational or operational errors. While the original suite could be used to test the upgrade, this might be time-consuming. The object of the work described in this paper is to derive an algorithm that will conduct only those tests which are really needed.

The proposed algorithm is briefly described in pseudocode, and the results of applying it to two example programs are given. In the first example, a saving of about 10 percent results, and in the second the saving is an impressive 95 percent. This is a useful paper.