'gfortran compiler error calling recursive log_gamma function

I uploaded a 2F1 hypergeometric function but it turns out that it does not compile on my computer. It is from this article. I use

GNU Fortran (Built by Jeroen for the R-project) 8.3.0

shiped with RTools 4.0. Can you figure out why it does not compile and how this could be solved? In the code below, I just kept the one line that generates the error. The error is given next.

MODULE HYP_2F1_MODULE
  !--------------------------------------------------------------------
  IMPLICIT NONE
  INTEGER, PARAMETER :: PR=KIND(1.0D0)
  REAL(PR)     ::  ONE=1.0D0
CONTAINS
  !
END MODULE HYP_2F1_MODULE
!
!----------------------------------------------------------------------
RECURSIVE FUNCTION LOG_GAMMA(Z) RESULT(RES)

  USE HYP_2F1_MODULE
  IMPLICIT NONE
  COMPLEX(PR),INTENT(IN) :: Z
  COMPLEX(PR)  :: RES
  !
     RES = LOG_GAMMA( ONE -z);
  !
END FUNCTION LOG_GAMMA

Here is the error message

 testZ.f90:18:22:

      RES = LOG_GAMMA( ONE - Z);
                 1
Error: 'x' argument of 'log_gamma' intrinsic at (1) must be REAL

fortran gfortran

Solution 1:^[1]

There is a Fortran 2008+ intrinsic of the same name

16.9.119 LOG_GAMMA (X)
1 Description. Logarithm of the absolute value of the gamma function.
2 Class. Elemental function.
3 Argument. X shall be of type real. Its value shall not be a negative integer or zero.

There is some sort of clash I do not completely understand here. The obvious workaround is to rename your function. What I can say is that without the result clause (which you need because of the recursive attribute) the intrinsic would be shadowed. It might be a compiler bug.

Also consider, whether the intrinsic of the same name couldn't also do what you need from your function.

Solution 2:^[2]

In addition to @VladimirF's suggestions, you can add the compiler flag -std=f95 to enforce compliance with the Fortran 95 standard. Provided you haven't added -fall-intrinsics this will disable all intrinsics from standards after Fortran 95, and should make the legacy code work.

Sources

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Source: Stack Overflow

Solution	Source
Solution 1
Solution 2	veryreverie

'gfortran compiler error calling recursive log_gamma function

Solution 1:[1]

Solution 2:[2]

Sources

Related Questions

Solution 1:^[1]

Solution 2:^[2]