Evaluate a function using a loop Fortran 90 - function

Question

I'm stuck in a process where I need to compute the values of a function f[x,y,z] on a grid. Here I put how I wrote the program, only evaluating on a one-dimensional grid.
I wrote the program:
program CHISQUARE_MINIMIZATION_VELOCITY_PROFILES
use distribution
IMPLICIT none
integer, parameter :: kp=1001 ! Parameter which states the number of points on the grid.
integer, parameter :: ndata=13 ! Parameter which states the number of elements of the data file.
integer, parameter :: nconst=3 ! Fixed integer parameter.
integer i, j, n
real*8 rc0, rcf, V00, V0f, d00, d0f, rc, V0, d, z
real*8 rcr(kp), V0r(kp), d0r(kp), chisq(kp)
!Scaling radius range
rc0=0.0d-5 ! kpc
rcf=1.0d2 ! kpc
call linspace(rc0,rcf,kp,rcr)
!**************If I call like this, it works normal*****************
!CHISQUARED(1.3d0, 130.2d0, 0.12d0, 1.0d0, 1.0d0, 2.0d0, 0.0d0, 0.0d0, 1, !ndata, nconst)
! **1.27000000000000 0.745818846396887**
! Press any key to continue
!**************If I call like this, it works normal*****************
!******* Here is where my problem is****************
do j=1, kp
rc=rcr(j)
write(*,*) rc, CHISQUARED(rc, 130.2d0, 0.12d0, 1.0d0, 1.0d0, 2.0d0, 0.0d0, 0.0d0, 1, ndata, nconst)
enddo
!******* Here is where my problem is****************
end program CHISQUARE_MINIMIZATION_VELOCITY_PROFILES
I use the module where I compute the chi^2 distribution, coming from a theoretical model...
MODULE distribution
IMPLICIT NONE
CONTAINS
! I define here the chi^2 function****
real*8 function CHISQUARED(rc, V0, d, alpha, gamma, chi, a, b, n, ndata, nconst)
integer i, n, ndata, nconst
real*8 rc, V0, d
real*8 alpha, gamma, chi, a, b, s
real*8, DIMENSION(ndata,3) :: X
open(unit=1, file="data.txt")
s=0.0d0
do i=1, ndata
Read(1,*) X(i,:)
s=s+((X(i,2)-VELOCITYPROFILE(X(i,1), rc, V0, d, alpha, gamma, chi, a, b, n))/(X(i,3)))**2.0d0
end do
CHISQUARED=s/(ndata-nconst)
end function CHISQUARED
!****Here I define the model function
real*8 function VELOCITYPROFILE(r, rc, V0, d, alpha, gamma, chi, a, b, n)
integer i, n
real*8 r, rc, V0, d, alpha, gamma, chi, a, b, z
if (rc < 0.0d0 .OR. d < 0.0d0 .OR. a <0.0d0 .OR. b <0.0d0 .OR. alpha < 0.0d0 .OR. gamma <0.0d0 .OR. chi < 0.0d0 .OR. n<1 ) then
VELOCITYPROFILE=0.0d0
return
else
z=0.0d0
do i=0,n
z=z+((V0*((r/rc)**(1.5d0))*(1+a+r/rc)**(-gamma*(2*n+0.5d0)))/((a+(r/rc)**alpha)**(chi/2.0d0)))*(((b+r/rc)**gamma)/d)**i
end do
VELOCITYPROFILE=z
end if
end function VELOCITYPROFILE
END MODULE distribution
!*****************END OF THE MODULE******************************
the data.txt file is of the form
0.24 37.31 6.15
0.28 37.92 5.5
0.46 47.12 3.9
0.64 53.48 2.8
0.73 55.14 3.3
0.82 58.47 2.5
1.08 66.15 3.3
1.22 69.39 2.75
1.45 74.55 5.
1.71 77.94 2.93
1.87 81.66 2.5
2.2 86.81 3.02
2.28 90.08 2.1
2.69 94.38 3.92
2.7 95.36 1.8
In order to get several values of the function CHISQUARED, I use the subroutine linspace to generate the partition of the 1-dimensional grid
subroutine linspace(xi,xf,jmax,y)
integer jmax,j
real*8 xi,xf,y(jmax)
y=(/(xi+dble(j-1)*(xf-xi)/(dble(jmax)-1.0d0), j=1, jmax)/)
end subroutine linspace
What happens is that if in the main program, I call the function CHISQUARED like this:
CHISQUARED(1.3d0, 130.2d0, 0.12d0, 1.0d0, 1.0d0, 2.0d0, 0.0d0, 0.0d0, 1, ndata, nconst)
**1.27000000000000 0.745818846396887**
Press any key to continue
I get some finite value, like, I don't know, 0.7 or something like this. (I restricted the data file so the result won't be the one written, I just put 0.7 as an example). However, when I put it inside a loop as it is in the program written above, to get the values on the one dimensional grid, it gives me the error
**0.000000000000000E+000 NaN**
forrtl: severe (24): end-of-file during read, unit 1, file C:\Users\Ernesto Lopez Fune\Desktop\Minimize\newone\chisquarerotationcurve\data.txt
Image PC Routine Line Source
chisquarerotation 0040B889 Unknown Unknown Unknown
Press any key to continue
Can anyone recommend me what to do in this case? How to overcome this barrier?

Answer 1

According to your error, you reach the end of your file.
When you call your subroutine once, it's OK but in a loop, your file is read multiple times. After the first iteration, your file is read until the EOF control but for the next iteration, the program can't read anymore because it has already reached the end of the file.
You need to use the REWIND(1) statement before end function CHISQUARED. With this, the cursor will be re-positioned at the beginning of the file. Besides, I think it would be better to OPEN your file in the main program and not in a function or subroutine to avoid multiple OPEN/CLOSE.
Don't forget to CLOSE your file when you are done dealing with it.