Lifegame in fortran

lifegame.f90

module lifegame
    implicit none
    integer :: W, H
    integer, allocatable :: field(:, :)
    integer, allocatable :: neighbors(:, :)
contains
    subroutine init_field(width, height, start_ratio)
        integer, intent(in) :: width, height
        double precision, intent(in) :: start_ratio
        double precision, allocatable :: s(:, :)
        W = width
        H = height
        allocate( field(W, H) )
        allocate( s(W, H) )
        call random_number(s)
        field = s + start_ratio
        allocate( neighbors(W, H) )
    end subroutine init_field

    subroutine print_field()
        implicit none
        integer :: n, i
        do i = 1, H
            write(*, '(*(i0,:," "))') field(:, i)
        enddo
    end subroutine print_field

    subroutine one_epoch
        implicit none
        integer :: dx, dy, i

        neighbors = 0
        do concurrent (dx = -1:1, dy = -1:1)
            neighbors = neighbors + cshift(cshift(field, dx, 1), dy, 2)
        enddo

        where(neighbors == 3)
            field = 1
        elsewhere(neighbors == 4)
            field = field
        elsewhere
            field = 0
        endwhere
  
    end subroutine one_epoch
end module lifegame

program flg
    use lifegame
    implicit none
    integer :: epoch, width, height
    integer :: i

    write(*, *) "# Width?"
    read(*, *) width
    write(*, *) "# Height?"
    read(*, *) height
    write(*, *) "# Epoch?"
    read(*, *) epoch

    call init_field(width, height, 0.5d0)
    call print_field
    
    do i = 1, epoch
        call one_epoch
        write(*, *)
        write(*, *)
        call print_field
    enddo 
    write(*, *)
    write(*, *)

    stop
end program flg

plotter.plt

reset
set key below

set nozeroaxis
set notics
unset colorbox

set size square

set term gif animate size 240,200
set output "field.gif"

set palette grey
do for [n=0:200:1] {
   p "field.log" i n mat w ima t sprintf("generation %d", n)
}

run.sh

#!/bin/bash

gfortran lifegame.f90
echo "64\n64\n512" | ./a.out > field.log
gnuplot plotter.plt