      subroutine slope(y,npts,xpk)

C  Remove best-fit slope from data in y(i).  When fitting the straight line,
C  ignore the peak around xpk +/- 2.

      real y(npts)
      real x(100)

      do i=1,npts
         x(i)=i
      enddo

      sumw=0.
      sumx=0.
      sumy=0.
      sumx2=0.
      sumxy=0.
      sumy2=0.

      do i=1,npts
         if(abs(i-xpk).gt.2.0) then
            sumw=sumw + 1.0
            sumx=sumx + x(i)
            sumy=sumy + y(i)
            sumx2=sumx2 + x(i)**2
            sumxy=sumxy + x(i)*y(i)
            sumy2=sumy2 + y(i)**2
         endif
      enddo

      delta=sumw*sumx2 - sumx**2
      a=(sumx2*sumy - sumx*sumxy) / delta
      b=(sumw*sumxy - sumx*sumy) / delta

      do i=1,npts
         y(i)=y(i)-(a + b*x(i))
      enddo

      return
      end

