function S = STFT_temp(x, w, sampling_freq, freq_step, sample_step)
len_w = length(w)-1;
len_x = length(x);

scrsz = get(0,'ScreenSize');
H1 = figure('Position',[(3*scrsz(3))/4 1  scrsz(3)/4 scrsz(4)/4]);

tv = 0:len_x-1;
tv = (1/sampling_freq).*tv;
Sx = [];
f1v = [];
for f1 = 0:freq_step:(sampling_freq/2)
   f1v = [f1v f1];
   figure(H1)
   title(f1)
   exp_fun = exp(-i*2*pi*f1.*tv);
   S1v = [];
   n1 = 1;
   while n1 < (len_x - sample_step - len_w - 1),
      S1 = (1/sampling_freq)*sum(x(n1:n1+len_w).*w.*exp_fun(n1:n1+len_w));
      S1v = [S1v S1];
      n1 = n1 + sample_step;
   end
   Sx = [Sx;S1v];
end

close(H1);
figure
subplot(211), plot(tv, x);
grid, title('signal');
xlabel('time (sec)'); ylabel('amplitude');
axis([0 max(tv) 1.5*min(x) 1.5*max(x)]);

Ss = size(Sx); Ss = Ss(1,2);
t1v = tv(1:sample_step:length(x)-sample_step-len_w-1); t1v = t1v(1:Ss);
subplot(212), imagesc(t1v, f1v, abs(Sx).^2); axis xy;
title('STFT'),
xlabel('time (sec)'); ylabel('frequency (Hz)');
S = Sx;

STFT of chirp signal

 
 

STFT of displacement signal