Modifying an array in fortran

Question

I have the following problem. I have a file that I must:

1. divide in cells to create an NxN grid;
2. counts the particles in each cell;
3. write the resulting numbers in a particular way.

The problem is the third point: I must write an NxN array each numbers represent the total numbers of particles in each cell, but I don't know how to write the file in an NxN array.

program eccen
    implicit none
    integer, parameter:: grid=200
    integer::i,j,k,n,m
    real*8,allocatable::f(:,:)
    real*8::xx(grid),yy(grid),mval,Mxval
    real*8,allocatable::x(:),y(:)

    open(10,file='coordXY.txt')
    n=0
    DO
       READ(10,*,END=100)
        n=n+1
    END DO

 100     continue
    rewind(10)

    allocate(x(n),y(n))

    do i=1, n
        read(10,*) x(i),y(i)
    end do

! create a grid
    mval=-15.
    Mxval=15.
    do i=1, grid
        xx(i) = mval + ((Mxval - mval)*(i-1))/(grid-1)
        yy(i) = mval + ((Mxval - mval)*(i-1))/(grid-1)
    end do

    open(20,file='fluxXY.dat')

! counts the paticles in each cell of the grid


    allocate(f(grid,grid))
    f=0
    do i=1,grid
        do j=1,grid
            m=0.
            do k=1, n
                if (x(k) > xx(i) .and. x(k) < xx(i+1) .and. &
                 & y(k) > yy(j) .and. y(k) < yy(j+1)) then  
                    m=m+1 ! CONTA IL NUMERO DI PARTICELLE
                end if
            end do
            f(i,j)=float(m+1)    
! THIS IS HOW I WRITE THE FILE BUT THIS SHOULD BE CHANGED
            write(20,*) f(i,:)

        end do
        write(20,*)
        print *,i
    end do    
end program eccen

Thanks a lot for Your help!

Answer 1

[SOLVED]

I finally solve all my problems:

1. using ifort with -no-wrap-margin -> work !

2. using ifort with @Stefan tips -> work!

3. use gfortran alone -> work !

The difference is in the file size: using the 1) solution the file is a bit larger than with the 2) solution. The 3) case, again, shows difference in file size respect the other cases (higher than the other two). Respectively:

1. 60kb;
2. 40kb;
3. 65kb.

For a test file with grid=50 and an input file of 4001 lines and 2 rows (132kb).

Thanks You all!!!!!

Answer 2

The Intel Fortran Compiler (ifort) performs an automatic wrapping which fits 3 double precision numbers, while gfortran does not.

You should create an explicit format (mentioned by @francescalus):

1000  FORMAT(<grid>F16.8)

In this format, the variable grid can be used directly. Now you can specify your WRITE statement as

write(20,1000) f(i,:)