program bifurcation_enlarge
      character*1 ch

      x_ini=0.5

      rmin=0.0
      rmax=1.0
      xmin=0.0
      xmax=1.0

      if(pgopen('/xwin')<=0)stop
c     call pgenv(rmin,rmax,0.0,1.0,0,0) 
c     call pglab('r','x','Bifurcation')
      call pgask(0)

 100  write(*,*)'How many generations?'
      read(*,*)n
      n_group_size=n/15

      call pgeras
      call pgenv(rmin,rmax,xmin,xmax,0,0)
      call pglab('r','x','Bifurcation (Enlarged)')

      dr=(rmax-rmin)/999
      do j=1,1000
        r=rmin+(j-1)*dr     

        x=x_ini

        do i=1,n
          x = 4*r*x*(1-x)
c          if(n<10)cycle
          call pgsci(i/n_group_size)
          call pgpt(1,r,x,-1)
        end do

      end do

      write(*,*)'Enlarge?(Yes=1,No=0)'
      read(*,*)i_enlarge
      if(i_enlarge==1) then
        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
      endif

      rmin=x1
      rmax=x2
      xmin=y1
      xmax=y2
      goto 100

 102  write(*,*)'Again?(Yes=1,No=0)'
      read(*,*)i_again
      if(i_again==1)goto 100
      if(i_again==0)stop
      goto 102 

      end