program polint_main

      real x_tab(20), y_tab(20), x_min, x_max, x_plot(200), y_plot(200)
      real delta_x, dy_plot(200)
      integer ntab, i, nplot, m, j, pgopen

      write(*,*)'Please tell me the number of tabulated values:'
      read(*,*) ntab

      open(unit=10, file='input_value.dat')
      do i=1,ntab
        read(10,*) x_tab(i), y_tab(i)
      end do      
      close(10)

      write(*,*) 'Type in min and max of x:'
      read(*,*) x_min, x_max

      write(*,*) 'How many points to draw ?'
      read(*,*) nplot

      write(*,*) 'How many point to form polynomial ?'
      read(*,*) m

      delta_x = (x_max - x_min) / (nplot - 1)

      do i=1, nplot
        x_plot(i) = x_min + (i-1) * delta_x
        call locate(x_tab,ntab,x_plot(i),j)
        k = min( max(j-(m-1)/2,1) , ntab+1-m )
        call polint(x_tab(k), y_tab(k), m, x_plot(i), y_plot(i),
     &       dy_plot(i))
      end do
      
      do i=1,nplot,10
        write(*,*) 'x_plot and y_plot,', x_plot(i), y_plot(i)
      end do

      if ( pgopen('?') .le. 0 ) stop
      call pgenv(2.0, 6.0, 0.0, 40.0, 0, 1)
      call pgline(nplot, x_plot, y_plot)
      call pgclos

      end