It is strongly suggested that users force all program variables to be explicitly typed. This is done by including the line “IMPLICIT NONE” as close to the first line as possible. Study some of the examples accompanying an IMSL Fortran Numerical Library routine early on. These examples are available online as part of the product.

Each subject routine called or otherwise referenced requires the “use” statement for an interface block designed for that subject routine. The contents of this interface block are the interfaces to the separate routines available for that subject. Packaged descriptive names for option numbers that modify documented optional data or internal parameters might also be provided in the interface block. Although this seems like an additional complication, many typographical errors are avoided at an early stage in development through the use of these interface blocks. The “use” statement is required for each routine called in the user’s program.

However, if one is only using the Fortran 77 interfaces supplied for backwards compatibility then the “use” statements are not required.