c----------------------------------------------------------------------
	subroutine rdff(n,r0,f,df)
c  differentiates a function of r from 0 to infinity on n
c  points using y=1/(1+r/r0), using 6-point formulas
c
c  author: updated by Kieron, 8.14.99
c      in: n - number of gripoints
c          r0 - parameter for scaled grid
c          f  - vector of function values
c     out: df - derivative of f
c  CALLS: stddff
	implicit real*8(a-h,o-z)
	dimension f(0:n),df(0:n)