title: write in array format in fortran
body: <p>I try to write an output file.dat with an <em>nxn</em> matrix format . </p>
  
  <p>I write the code but the output is a column of value f.</p>
  
  <p>Now the problem is: how can i change the output-format of the file to write?</p>
  
  <p>from:
   1
   2
   4
   5
   ...</p>
  
  <p>to: 1,2,3,4 //
      5,6,8,.. //</p>
  
  <pre><code>program eccen
      implicit none
      integer, parameter:: grid=800
      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='3d_disk.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
  
  
      mval=-20.
      Mxval=20.
      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='3d_map.dat')
  
      allocate(f(n,n))
      f=0
      do i=1,grid
          do j=1,grid
              m=0.
              do k=1, n
                  if (x(k) &gt; xx(i) .and. x(k) &lt; xx(i+1) .and. &amp;
                   &amp; y(k) &gt; yy(j) .and. y(k) &lt; yy(j+1)) then  
                      m=m+1 ! CONTA IL NUMERO DI PARTICELLE
                  end if
              end do
              f(i,j)=float(m+1)
  </code></pre>
  
  <p>I thing that the modification must be here from this:</p>
  
  <pre><code>                write(20,*) f(i,j)
              end do
              write(20,*)
       print *,i
          end do    
  end program eccen
  </code></pre>
  
  <p>to:</p>
  
  <pre><code>    do i=1,grid
        do j=1,grid
          write(20,*) f(i,j)
        end do
      end do
  
  end do
              write(20,*)
       print *,i
          end do
  
   end program eccen
  </code></pre>