function S=simpson2(x,y)
  n=length(x)
  h=x(2)-x(1)
  s=y(1)+y(n)
 for i=2:n-1
   if rem(i,2)==0
     s=s+4*y(i)
   else s=s+2*y(i)
   endif
 endfor
 S=h/3*s
endfunction