Top-down synthesis of simple divide and conquer algorithms

Abstract

A new method is presented for the deductive synthesis of computer programs. The method takes as given a formal specification of a user's problem. The specification is allowed to be incomplete in that some or all of the input conditions may be omitted. A completed specification plus a computer program are produced by the method. Synthesis involves the top-down decomposition of the user's problem into a hierarchy of subproblems. Solving each of these subproblems results in the synthesis of a hierarchically structured program. The program is guaranteed to satisfy the completed specification and to terminate on all legal inputs. In this paper we present a framework for a top-down synthesis process, explore the structure of a class of divide and conquer algorithms, and present a method for the top-down synthesis of algorithms in this class. Detailed derivations of four sorting algorithms are presented. (Author)