IMSL Fortran Library routines have required arguments and may have optional arguments. All arguments are documented for each routine. For example, consider the routine ORDST that determines order statistics. The required arguments are X, NOS, OS, and NMISS. The input data for the problem are the X array and NOS, the number of order statistics; the output is returned in the OS array. The number of missing values is returned in NMISS. This routine has as optional arguments NOBS, IOPT, and IOS. If one wishes to calculate a different set of order statistics than the default (the first NOS order statistics) then the optional argument given by the “IOPT=” keyword should be used in the argument list. See Example 2 of ORDST in Chapter 1, “Basic Statistics” for an example of this functionality.

For compatibility with previous versions of the IMSL Libraries, the NUMERICAL_LIBRARIES interface module includes backwards compatible positional argument interfaces to all routines which existed in the Fortran 77 version of the Library. Note that it is not necessary to use “use” statements when calling these routines by themselves. Existing programs which called these routines will continue to work in the same manner as before.