%  function name：FT
%  [X,w]=ft(x,t,W)
%  This program is used to compute the Fourier transform of a
%  continuous-time signal x(t)
%  x: The continous-time signal, vector
%  t: The time vector corresponding x
%  W: The range of frequency: -W~W, radians/sec 
%  X: Returned Fourier transform X of x, it is complex vector
%  w: Returned frequency vector corresponding X, radians/sec
function [X,w]=ft(x,t,W)
p=t(2)-t(1);
N=512;           
k=-N:N; 
w=k*W/N; 
X=x*exp(-j*t'*w)*p;