program logistic_map

      write(*,*)'What is your r value?'
      read(*,*)r
      write(*,*)'What is your initial x value?'
      read(*,*)x
      write(*,*)'How many generations?'
      read(*,*)n

      xmax=n
      if(pgopen('/xwin')<=0)stop
      call pgenv(0.0,xmax,0.0,1.0,0,0) 
      call pgmove(1.0,x)

      do i=1,n
        x = 4*r*x*(1-x)
        g=i+1
        call pgdraw(g,x)
      end do

      call pgclos

      end