A function reference is invoking a subroutine

Question

I have CERN program which calculates the gamma function of complex argument, but I can't run the program because of lack of Fortran knowledge.

I have the following program:

PROGRAM Console1
  IMPLICIT REAL *8 (A-H,O-Z) 
  COMPLEX *16 gama,z,w 
  z=cmplx(0,0.707106781186548d0) 
  gama=cgamma(0,z,w) 
END

SUBROUTINE cgamma(mo, z, w) 
  INTEGER, PARAMETER :: dp = SELECTED_REAL_KIND(14, 60)
  INTEGER, INTENT(IN)       :: mo
  COMPLEX (dp), INTENT(IN)  :: z
  COMPLEX (dp), INTENT(OUT) :: w
... the subroutine code here 
END SUBROUTINE cgamma

and then error appears

error #6553: A function reference is invoking a subroutine subprogram. [CGAMMA]

Answer 1

Look at the error message:

A function reference is invoking a subroutine subprogram.

SUBROUTINE cgamma(mo, z, w)
END SUBROUTINE

defines cgamma as a (in this case external) subroutine.

In the program

gama=cgamma(0,z,w)

references cgamma as a function (returning a result to be assigned to gama). This is the incompatibility to which the error message refers.

To resolve this you need to reference the subroutine with a call statement, or change cgamma to be a function, returning an appropriate result.

Given the design of the procedure (three arguments) I'd expect the function is intended.