Subroutine Example

• A subroutine is invoked by a CALL statement as in:

    CALL sub1(arg1,arg2,arg3)

  arg1, arg2 and arg3 are actual arguments.
• a, b and c are dummy arguments and must match the actual arguments in type, rank, kind and number.

    SUBROUTINE sub1(a,b,c)
     IMPLICIT NONE
     REAL :: a, b, c, s
       ...
      CALL sum_sq(a,b,c,s)
       ...
    CONTAINS
     SUBROUTINE sum_sq(aa,bb,cc,ss)
      REAL, INTENT(IN) :: aa, bb, cc
      REAL, INTENT(OUT) :: ss 
       ss = aa*aa + bb*bb + cc*cc
     END SUBROUTINE sum_sq
    END SUBROUTINE sub1

• the above shows any external subroutine can invoke one of its own internal procedures,
• external subroutines should be declared,

     EXTERNAL sub1

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