Subroutine plprme (xx,y,n)
c *** see RH Landau, Program lpott, 1981
c     plprme calculates the deriv of the legrendre polynl,all l
      Implicit  Real*8   (a-h,o-z)
      Dimension y(50)
      y(1) = 0.
      y(2) = 1.
      If (n.le.2) Return
      Do 10 i=2,n
         y(i+1) = ((2*i-1.)*xx*y(i)-i*y(i-1))/(i-1)
 10   Continue
      Return
      End