VMS Help FORTRAN, Intrinsic Procedures, IDIM  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  IDIM (number, number)

  A function that returns the value of the first argument minus the
  minimum (MIN) of the two arguments.

  +------+---------+----------+------------+-------------+
  | Args | Generic | Specific |  Argument  | Result Type |
  +------+---------+----------+------------+-------------+
  |  2   |  IDIM   | IIDIM    | INTEGER*2  | INTEGER*2   |
  |      |         | JIDIM    | INTEGER*4  | INTEGER*4   |
  +------+---------+----------+------------+-------------+
  See also the DIM intrinsic function.