FORTRAN routines with optional arguments

In designing a general purpose subroutine package to solve a class of problems, one often has to write subroutines with a large number of arguments. Although these arguments are required to cover a range of possibilities, many of these arguments have some commonly occurring values. The user is thus burdened with supplying a long list of arguments and making sure that the number and types match. An alternate solution is to write such subroutines in assembly language so that they could have a variable number of arguments. This approach is expensive and eliminates a large class of program designers who do not and do not want to know assembler language. This paper describes a facility which enables these program designers to write their routines completely in a higher level language (FORTRAN) and yet enjoy the ‘luxury’ of having a variable number of arguments in the calling sequence.