Search code examples
fortrangfortranlapack

'dlantr' at (1) is not a function

I'm facing an odd problem while trying to use Lapack function dlantr to compute norm of triangular matrix. Basically, I had a working single-file program with dlantr and some other Lapack procedures in it, and now I want to split it into modules. dlantr ended in subroutine in one such module. However, trying to compile said module with gfortran-10 (through MPI wrapper compiler, since there's also some MPI in there) like

mpifort -o kde.o -c kde.f90

leads to an error :

‘dlantr’ at (1) is not a function

which is strange, because

  • other Lapack procedures (in my case dtrtri and dpotrf) in the same subroutine work alright
  • a simple subroutine in a same module like
subroutine foo(a)
    real(kind=DP), intent(in) :: a(2,2)
    real(kind=DP) :: tmp, dlantr
    print*, dlantr('F','L','N',2,2,a,2,tmp)**2
end subroutine

also works fine when called from the main program. In the subroutine where the problem arises, it is declared in the same way as above and in the original program, that is real(kind=DP) :: ..., dlantr, ...

The code in question can be found here. What could be causing such behaviour, and how to fix it?

Solution

  • My original answer was wrong. This is a compiler bug, probably https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87127. Still, this workaround of explicitly using the external attribute makes the error go away:

        real(kind=DP), external :: dlantr

    The MWE for this bug is:

    subroutine sub
    integer :: d
    real :: f
    real :: a
    
    associate (c => d)
        a = f()
    end associate
end subroutine sub