How to create function inside a Fortran subroutine?

Question

When I compile my code, the result is strange (very large as -1.112E+09). When I calculate by Matlab, the answer is -0.0873.

program test
real, parameter :: X11=10,X22=5,X33=5,BE1A1=2,BE1B1=2
real :: Y

call J(X11,X22,X33,BE1A1,BE1B1,M)
Y = M
print *,Y

end program test

  subroutine J(X1,X2,X3,BE1A1,BE1B1,M)

    real, intent(in) :: X1,X2,X3,BE1A1,BE1B1
    real, intent(out) :: M

    M = J1(X1,X2,X3,BE1A1,BE1B1)-J1(X1,X2,X3,BE1A1,-BE1B1)-J1(X1,X2,X3,-BE1A1,BE1B1)+J1(X1,X2,X3,-BE1A1,-BE1B1)

    contains

    real function J1(X1,X2,X3,EPS1,EPS2)

    real, intent(in) :: X1,X2,X3,EPS1,EPS2
    real :: R
    R = sqrt((X1-EPS1)**2+(X2-EPS2)**2+(X3)**2)
    J1 = log(R+X2-EPS2)

    end function J1

  end subroutine J

You should be aware of implicit typing rules. In particular for `m` in the main program. — francescalus, Dec 14 '15 at 02:02

score 2 · Answer 1 · answered Dec 14 '15 at 02:14

program test

real, parameter :: X11=10,X22=5,X33=5,BE1A1=2,BE1B1=2
real :: Y

call J(X11,X22,X33,BE1A1,BE1B1,CM)
Y = CM
print *,Y

end program test

  subroutine J(X1,X2,X3,BE1A1,BE1B1,CM)

    real, intent(in) :: X1,X2,X3,BE1A1,BE1B1
    real, intent(out) :: CM

    CM = J1(X1,X2,X3,BE1A1,BE1B1)-J1(X1,X2,X3,BE1A1,-BE1B1)-J1(X1,X2,X3,-BE1A1,BE1B1)+J1(X1,X2,X3,-BE1A1,-BE1B1)

    contains

    real function J1(X1,X2,X3,EPS1,EPS2)

    real, intent(in) :: X1,X2,X3,EPS1,EPS2
    real :: R
    R = sqrt((X1-EPS1)**2+(X2-EPS2)**2+(X3)**2)
    J1 = log(R+X2-EPS2)

    end function J1

  end subroutine J

Now I can obtain the same result with Matlab!

The could would still be safer with `implicit none`. And please make somehow clear what you changed, it is difficult to find it in the code. — Vladimir F Героям слава, May 04 '17 at 06:43

How to create function inside a Fortran subroutine?

1 Answers1