program bifurcation

      x_ini=0.5

      rmin=0.0
      rmax=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,0.0,1.0,0,0)
      call pglab('r','x','Bifurcation')

      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

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

      end