c/* %W%      latest revision %G% %U% */
      subroutine pldblp(xx,y,n)
************************************************************************

c     calculates the second derivative of the legendre pol,all l
c      taking derivative of eqs 3.28 3.29 jackson elimhna
c      tingdpl/dx

      implicit real*8 (a-h, o-z)

      dimension y(100)

c >>> FIRST EXECUTABLE STATEMENT <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<

      y(1)=0.
      y(2)=0.
      y(3)=3.
      if(n.le.3) return
        nn=n-1
      do 2 i=3,nn
   2    y(i+1)=((2*i-1)*xx*y(i)-(i+1)*y(i-1))/(i-2)
      return
c**  this program valid on ftn4 and ftn5 **
      end