function y=sgn(x)
%% function y=sgn(x)
%%    sign function 
%%    sign(x)  = 1 if x>0
%%               0  if x=0
%%               -1  if x<0
%%    x  input time pts
%%    y   output response
%%  Copyright (C) Jin-Ting Zhang, Dept of Stat & Appl. Prob., NUS, Singapore
%%      16/01/2002

y=(x>0)-(x<0);