program bifurcation_n_enlarge
      implicit none
      real r,x_ini,x,xi
      integer pgopen,i,i_again,isymbol,n_gen,j,n_group_size
      integer idummy,pgband
      real r_min,r_max,x_min,x_max,x_pos,y_pos,x1,x2,y1,y2,temp
      character*(1) ch

      isymbol = -1

      write (*,*) 'This plots fix-points x* of x_n+1=4rx_n(1-x_n+1).'
      write (*,*)
c     write (*,*) 'What is the initial value of x (0 < x < 1) ?'
c     read (*,*) x_ini
      x_ini = 0.5

      if ( pgopen('/xwin') .le. 0 ) stop
c     call pgpap(5.0,0.75)
c pgask(0) means not to ask confirmation when erase a page
      call pgask(0)

 100  write (*,*) 'What is the numer of generation for the mapping ?'
      read (*,*) n_gen

      call pgeras
      call pgsci(1)
      r_min=0.0
      r_max=1.0
      x_min=0.0
      x_max=1.0
 200  call pgenv(r_min, r_max, x_min, x_max, 0, 0)

      n_group_size = n_gen/15

      do j=1,1000
      r = r_min + j*(r_max-r_min)/1000
      x = x_ini
      call pgbbuf
        do i=1,n_gen
          x = 4*r*x*(1-x)
          call pgsci(i/n_group_size)
c         if (i.gt.(0.1*n_gen)) call pgpt(1,r,x,isymbol)
          call pgpt(1,r,x,isymbol)
        end do
      call pgebuf
      end do

      write (*,*) 'Enlarge some parts ? (1=YES;0=NO)'
      read (*,*) i_again
      if (i_again.eq.0) goto 102

      write (*,*) 'Now choose a range to enlarge using mouse pointer.'
      write (*,*)
      idummy = pgband (0, 1, 0.5, 0.5, x_pos, y_pos, CH)
      x1 = x_pos
      y1= y_pos 
      idummy = pgband (2, 1, x1, y1, x_pos, y_pos, CH)
      x2 = x_pos
      y2 = y_pos

      if (x1.gt.x2) then
        temp = x1
        x1 = x2
        x2 = temp
      endif
      if (y1.gt.y2) then
        temp = y1
        y1 = y2
        y2 = temp
      endif

      write (*,*) 'Your choice is: ', ' r = (',x1,'~',x2,' y = (',y1,'~'
     &,y2,')'

      r_min = x1
      r_max = x2
      x_min = y1
      x_max = y2

      write (*,*) 'What is the numer of generation for the mapping ?'
      read (*,*) n_gen
      goto 200

 102  write (*,*) 'Again ? (1=YES;0=NO)'
      read (*,*) i_again
      if (i_again.eq.1) goto 100
      if (i_again.eq.0) stop
      goto 102

      end