problem with my results

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raj 2012-2-2

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https://ww2.mathworks.cn/matlabcentral/answers/27767-problem-with-my-results

编辑： Jon 2013-9-26

I am plotting a spectrogram using STFT algorithm generated by me everything works fine but my results are not what i expected please help me where I am wrong.

clear all
close all
clc
Fs = 2*max(100,300);
t = 0:1/Fs:1-1/Fs;
t1 = t(end);
x = chirp(t,300,t1,100,'linear');
w = rectwin(10)';
nw= length(w);
X = fft(x);
Total = [];
y = length(x) - nw;
for tau = 0: y
  S = 0;
  if tau == 0 %1st window
      S = X(1:nw);
    else %THE remaining windows generated from here
     for k = 0:nw-1
        for n = 0:nw-1
        S= (exp(2*pi*1j*k/nw).*(X(tau : tau + nw-1) -  x(tau)+...
                      x(nw+tau).*exp(-2*pi*1j*n/nw)));
        end
     end
    end
    W= S(1:end/2);
   Total = [Total; W];
end
%plotting
T = 1:length(x)/2;
imagesc(T,1:Fs/2,20*log10(abs(Total).^2))
axis xy; axis tight; colormap(jet);
xlabel('Time in sec');
ylabel('Frequency (Hz)');