Error with argument and procedure - visual-studio-2010

Question

I have to use a subroutine (neqnf) included in IMSL library, which let me solve non-linear systems. (link to users manual, neqnf page here)
main.f90, is:
program prova_sistema_in_un_modulo
include "link_fnl_shared.h"
use neqnf_int
use modx
implicit none
call d_neqnf(FCN, x, xguess=x_guess, fnorm=f_norm)
end program prova_sistema_in_un_modulo
where subroutine FCN is coded in an external module, modx.f90:
module modx
implicit none
integer, parameter :: ikind = selected_real_kind(8,99)
integer :: n=3
real(kind=ikind) :: f_norm
real(kind=ikind), dimension(3) :: x, x_guess=(/ 4.0, 4.0, 4.0/)
contains
subroutine FCN(x,f,n)
integer :: n !dummy var
real(kind=ikind), dimension(3) :: x, f !dummy var
f(1)=x(1)+A(x(1))+(x(2)+x(3))*(x(2)+x(3))-27.0 ! =0
f(2)=B(x(1),x(2))+x(3)*x(3)-10.0 ! =0
f(3)=Z(x(2),x(3)) ! =0
end subroutine FCN
function A(x)
real(kind=ikind) :: x !dummy var
real(kind=ikind) :: A !function var
A=exp(x-1.0)
end function A
function B(x,y)
real(kind=ikind) :: x,y !dummy var
real(kind=ikind) :: B !function var
B=exp(y-2.0)/x
end function B
function C(x)
real(kind=ikind) :: x !dummy var
real(kind=ikind) :: C !function var
C=sin(x-2.0)
end function C
function Z(x,y)
real(kind=ikind) :: x,y !dummy var
real(kind=ikind) :: Z !function var
Z=y+C(x)+x*x-7.0
end function Z
end module modx
but I get these three errors:
Error 1 error #7061: The characteristics of dummy argument 1 of the associated actual procedure differ from the characteristics of dummy argument 1 of the dummy procedure. (12.2) [FCN]
Error 2 error #7062: The characteristics of dummy argument 2 of the associated actual procedure differ from the characteristics of dummy argument 2 of the dummy procedure. (12.2) [FCN]
Error 3 error #7063: The characteristics of dummy argument 3 of the associated actual procedure differ from the characteristics of dummy argument 3 of the dummy procedure. (12.2) [FCN]
NB: if I put all code in the main program, all goes fine! while if I code using module (as I've done, the actually posted code) I get that errors!
can anyone help me?

Answer 1

The problem is that you provide a fixed dimension for the dummy arguments x(3) and f(3) in your custom function FCN, while IMSL expects a variable dimension x(n), f(n):
subroutine FCN(x,f,n)
integer :: n !dummy var
! real(kind=ikind), dimension(3) :: x, f !<- wrong
real(kind=ikind), dimension(n) :: x, f !<- correct
f(1)=x(1)+A(x(1))+(x(2)+x(3))*(x(2)+x(3))-27.0 ! =0
f(2)=B(x(1),x(2))+x(3)*x(3)-10.0 ! =0
f(3)=Z(x(2),x(3)) ! =0
end subroutine FCN
A working example to reproduce this is (interface borrowed from HYBRD1):
module test_int
contains
subroutine final(FCN, x, f, n)
interface
SUBROUTINE FCN (X, F, N)
INTEGER N
DOUBLE PRECISION X(N), F(N)
END SUBROUTINE
end interface
integer :: n
double precision :: x(n), f(n)
call FCN(x,f,n)
end subroutine
end module
module test_fct
contains
subroutine FCN(X, F, N)
integer :: n
double precision :: x(n), f(n)
print *,X ; print *,F ; print *,N
end subroutine
end module
program prova
use, intrinsic :: iso_fortran_env
use test_int
use test_fct
implicit none
integer,parameter :: n=2
double precision :: x(n), f(n)
x = [ 1.d0, 2.d0 ]
f = [ 3.d0, 4.d0 ]
call final(FCN, x, f, n)
end program prova