Infinity in Fortran

Question

What is the safest way to set a variable to +Infinity in Fortran? At the moment I am using:

program test
  implicit none
  print *,infinity()
contains
  real function infinity()
    implicit none
    real :: x
    x = huge(1.)
    infinity = x + x
  end function infinity
end program test

but I am wondering if there is a better way?

Answer 1

If your compiler supports ISO TR 15580 IEEE Arithmetic which is a part of so-called Fortran 2003 standard than you can use procedures from ieee_* modules.

PROGRAM main

  USE ieee_arithmetic

  IMPLICIT NONE

  REAL :: r

  IF (ieee_support_inf(r)) THEN
    r = ieee_value(r,  ieee_negative_inf)
  END IF

  PRINT *, r

END PROGRAM main