How to Make a Variable Global in mnbrak.f90?

[winiepu]

The following code is just an example. I try to apply mnbrak.f90 to my function f=(x-i)^2. I want to make i globle variable. If I use internal procedure, I can not use mnbrak.f90, since it can not accept the internal procedure. How do I deal with it? Thanks!

PROGRAM xbrent
USE nr
USE nrtype
IMPLICIT NONE

INTEGER(i4b) :: i
REAL(sp) :: ax, bx, cx, fa, fb, fc
!real, external:: f
! common i

DO i=1,10
ax=i-0.5_sp
bx=i+0.5_sp
CALL mnbrak(ax, bx, cx, fa, fb, fc, f)
!$ WRITE(*,'(1x,t13,a,t25,a,t37,a)') 'A','B','C'
!$ WRITE(*,'(1x,a3,t5,3f12.6)') 'X',ax,bx,cx
!$ WRITE(*,'(1x,a3,t5,3f12.6)') 'F',fa,fb,fc
write(*,*) f(ax),f(bx)
END DO

contains

FUNCTION f(x)
USE nr
USE nrtype
IMPLICIT NONE
REAL(sp) ::f,x
!common i
f=(x-i)**2.0_sp
END FUNCTION f

END PROGRAM xbrent

 

[lofgran]

Thank you for sharing your code and question. It seems like you are trying to use the mnbrak.f90 subroutine with your own function f=(x-i)^2, where i is a global variable. However, you are having trouble using an internal procedure with the mnbrak subroutine.

One solution to this issue could be to declare the global variable i as a module variable. This way, it can be accessed by both the main program and the internal procedure. You can do this by creating a module that contains the variable i and then importing it into both the main program and the internal procedure. Here is an example:

MODULE globals
INTEGER(i4b) :: i ! declare i as a module variable
END MODULE globals

PROGRAM xbrent
USE nr
USE nrtype
USE globals ! import the module containing i
IMPLICIT NONE

REAL(sp) :: ax, bx, cx, fa, fb, fc

DO i=1,10
ax=i-0.5_sp
bx=i+0.5_sp
CALL mnbrak(ax, bx, cx, fa, fb, fc, f)
WRITE(*,'(1x,a3,t5,3f12.6)') 'X',ax,bx,cx
WRITE(*,'(1x,a3,t5,3f12.6)') 'F',fa,fb,fc
write(*,*) f(ax),f(bx)
END DO

contains

FUNCTION f(x)
USE nr
USE nrtype
USE globals ! import the module containing i
IMPLICIT NONE
REAL(sp) ::f,x
f=(x-i)**2.0_sp
END FUNCTION f

END PROGRAM xbrent

By declaring i as a module variable, it can now be used in both the main program and the internal procedure. I hope this helps with your code! Let me know if you have any further questions.

 

[quicknote]

It seems like you are trying to make the variable "i" a global variable in your code. However, using an internal procedure in mnbrak.f90 prevents you from doing so. One solution to this problem could be to pass the value of "i" as a parameter to the function f instead of trying to make it a global variable. This way, you can still use the mnbrak.f90 subroutine without any issues. Another option could be to declare "i" as a module variable, which can be accessed by both the main program and the internal procedure. This would also allow you to use mnbrak.f90 without any problems.