      function upot(x)
      b1=-.6980
      b2=-.5839
      b3=-.0784
      b4=0.1675
      b5=1.0046
      b6=-.8693
      d=.4125383619
      s=x/(x+1.0)
      upot=1.0+s*(b1+s*(b2+s*(b3+s*(b4+s*(b5+s*b6)))))
      b0=315377.5
      upot=upot*s*s*b0
      return
      end
