HEQS — A hierarchical equation solver

HEQS is a set of tools for numerically solving sets of algebraic equations from their description in a text file. It allows users to compactly define (or alter an already defined) set of equations (a model), and then analyze and solve it with minimal intervention. HEQS automatically checks the algebraic and logical consistency of the equations, reports errors, and allows users to correct the errors by simply changing the original textual description of the relevant equations. HEQS can deal with unsubscripted or multiply subscripted (array) variables. Because it relieves users of the need to perform repetitive algebraic substitution and evaluation, it is most useful for sets of equations involving from tens to thousands of variables. HEQS commands can be used (1) interactively, to define and solve models, or (2) as a set of UNIX™ operating system high-level algebraic tools for building applications that require model solving. This paper describes the motivation and design of HEQS, illustrates its use, and highlights its underlying algorithms.