function l2=l(x0,x1,x2,x3,y1,y2,y3)
  l2=(((x0-x2)*(x0-x3))/((x1-x2)*(x1-x3)))*y1+(((x0-x1)*(x0-x3))/((x2-x1)*(x2-x3)))*y2+(((x0-x1)*(x0-x2))/((x3-x1)*(x3-x2)))*y3
  end
