function csevl (x, cs, n)
c april 1977 version.  w. fullerton, c3, los alamos scientific lab.
c
c evaluate the n-term chebyshev series cs at x.  adapted from
c r. broucke, algorithm 446, c.a.c.m., 16, 254 (1973).  also see fox
c and parker, chebyshev polys in numerical analysis, oxford press, p.56.
c
c             input arguments --
c x      value at which the series is to be evaluated.
c cs     array of n terms of a chebyshev series.  in eval-
c        uating cs, only half the first coef is summed.
c n      number of terms in array cs.
c
      dimension cs(1)
c
      if (n.lt.1) call seteru (28hcsevl   number of terms le 0, 28, 2,2)
      if (n.gt.1000) call seteru (31hcsevl   number of terms gt 1000,
     1  31, 3, 2)
      if (x.lt.(-1.1) .or. x.gt.1.1) call seteru (
     1  25hcsevl   x outside (-1,+1), 25, 1, 1)
c
      b1 = 0.
      b0 = 0.
      twox = 2.*x
      do 10 i=1,n
        b2 = b1
        b1 = b0
        ni = n + 1 - i
        b0 = twox*b1 - b2 + cs(ni)
 10   continue
c
      csevl = 0.5 * (b0-b2)
c
      return
      end