Modifying an array in fortran

Question

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

divide in cells to create an NxN grid;
counts the particles in each cell;
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!

Even after studying your sample program I must admit to still not understand what is being asked here. Are you asking how to represent a multidimensional array (a matrix, so to say) and how to write it out? — Rook
– Rook, Commented Jan 16, 2014 at 21:50
@ Idigas: Yes, a matrix of gridgrid (grid is the numbers of cells in x and y axes). But in my program the file in unit 20 has only 3 columns and a lot of lines. I want, however, an array with gridgrid (columns*lines) — Fornax-A
– Fornax-A, Commented Jan 16, 2014 at 23:13
Without knowing how those three columns look it's hard to say, but try writing with an explicit format. — francescalus
– francescalus, Commented Jan 17, 2014 at 8:38
Do you want the data to be formatted or unformatted? Are you sure there are only 3 columns? Switch off the line wrap on your editor - is it still 3 columns? — cup
– cup, Commented Jan 17, 2014 at 10:01
to @cup , yes because i put the output.dat in a program that read only NxN files and give me errors that demonstrate me the file is written as an Mx3 rray, where M is a very high number higher of N or (or using my f90 code syntax) higher of grid. — Fornax-A
– Fornax-A, Commented Jan 17, 2014 at 16:56

Stefan · Accepted Answer · 2014-01-17 11:07:54Z

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,:)

answered Jan 17, 2014 at 11:07

Stefan

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1 Comment

francescalus Over a year ago

ifort has the -no-wrap-margin compile flag (different spelling for Windows). <n> isn't portable, but there are ways around that (including *(F...) if one can call that portable).

Fornax-A · Accepted Answer · 2014-01-17 18:09:15Z

0

[SOLVED]

I finally solve all my problems:

using ifort with -no-wrap-margin -> work !
using ifort with @Stefan tips -> work!
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:

60kb;
40kb;
65kb.

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

Thanks You all!!!!!

answered Jan 17, 2014 at 18:09

Fornax-A

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