subroutine Splint(xa,ya,y2a,n,x,y)
c
c     Spline interpolation  adapted from Numerical Recipes.
c     Give a value y at x. input xa(n) is equally distributed.
c     re-tested on 20/6/97 by Lu. 
c     note that x must be smaller xa(n)!!! otherwise set y = 0.

      implicit double precision (a-h,o-z)
      integer n, klo, k
      dimension xa(n),ya(n),y2a(n)
      
      if (x .gt. xa(n)) then
         y = 0.0d0
         return
         endif

      klo=1
      khi=n
1     if (khi-klo.gt.1) then
        k=(khi+klo)/2
        if(xa(k).gt.x)then
          khi=k
        else
          klo=k
        endif
      goto 1
      endif
      h=xa(khi)-xa(klo)
      if (h.eq.0.) pause 'bad xa input.'
      a=(xa(khi)-x)/h
      b=(x-xa(klo))/h
      y=a*ya(klo)+b*ya(khi)+
     *      ((a**3-a)*y2a(klo)+(b**3-b)*y2a(khi))*(h**2)/6.
      return
      end