C NCLFORTSTART
      subroutine taper_ncl (x,n,p,xt,iopt)
      implicit none
C NCL: xTaper = taper(x,p,iopt)
 
c this subroutine applies split-cosine-bell tapering tothe series x.
c .   the series will be tapered to the mean of x.
c .   See Bloomfield's "Intro to Fourier .."
c .   This is used prior performing an fft on non-cyclic data
 
c arguments:
c .   x   series to be tapered (tapering done in place)
c .       **missing data not allowed**
c .   n   series length
c .   p   the proportion of the time series to be tapered [p=0.10 means 10 %]
c .   xt  tapered series
c .   iopt option not used ... set to zero
C                                            INPUT
      integer n, iopt
      real x(n), p
C                                            OUTPUT
      real xt(n)
C NCLEND
      integer i, m
      real    weight, pi, pim, xav
      data pi /3.141592653589/

      xav = 0.0
      do i=1,n
         xt  = x(i)
         xav = xav+x(i)
      end do
      xav = xav/n
 
      m   = max0( 1 , int(p*float(n)+0.5)/2 )
      pim = pi/float(m)

      do i=1,m
         weight    = 0.5-0.5*cos(pim*(float(i)-0.5) )
         xt(i)     = (x(i)-xav)*weight + xav
         xt(n+1-i) = (x(n+1-i)-xav)*weight + xav
      enddo

c .   cft correction factor for taper (not used , for info only)
c c c cft = 0.5*(128.-93.*p)/(8.-5.*p)**2

      return
      end