On the design of a user interface to large Fortran subroutine packages under IBM 360/370 OS

An often encountered inconvenience when one uses a large subroutine package (e.g. IBMSSP) is that one faces the problem of selecting the proper subroutines in the proper sequence to execute the proper computation. This at times is difficult if not prohibitive because the algorithms employed by the subroutines are sophisticated and beyond the comprehension of the user. When this happens, the subroutine package becomes a frustration as much as a useful tool to the user. It is therefore desirable to split up such large subroutine packages into chapters of subroutines according to their functions and create control routines for each chapter. The purpose of these control routines is to interpret the arguments supplied by the user and then invoke the proper subroutines in the proper sequence for the computational solution.