The following example is valid for all source forms:

  Column:

  12345678...                                                            73
  _________________________________________________________________________

  ! Define the user function MY_SIN

        DOUBLE PRECISION FUNCTION MY_SIN(X)
          MY_SIN = X - X**3/FACTOR(3) + X**5/FACTOR(5)                    &
       &          - X**7/FACTOR(7)
        CONTAINS
          INTEGER FUNCTION FACTOR(N)
           FACTOR = 1
           DO 10 I = N, 1, -1
    10     FACTOR = FACTOR * I
          END FUNCTION FACTOR
        END FUNCTION MY_SIN