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How to calculate the phase spectrum of the square wave with fft?

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summer
summer on 29 Sep 2015
there is an article said that the phase spectrum is π or 0. I don't know it's right or not. so i used fft function to check it. the result is not same as the article.the matlab code is below, is there something wrong?thank you very much.
if true
Fs=1e2;
N=100;
t=0:1/Fs:(N-1)/Fs; %计算时间范围
S=[zeros(1,25) ones(1,50) zeros(1,25)];% %
subplot(3,1,1);plot(t,S);
N=length(S);
plot(S);
title('original signal');
figure;
Y = fft(S,N); %做FFT变换
Ayy = (abs(Y)); %取模
figure;
Ayy=Ayy/(N/2); %换算成实际的幅度
Ayy(1)=Ayy(1)/2;
F=Fs/N*([1:N]-1); %换算成实际的频率值
plot(F(1:N/2),Ayy(1:N/2)); %显示换算后的FFT模值结果
title('magnitude spectra ');
figure;
Pyy=angle(Y);
plot(F(1:N/2),Pyy(1:N/2)); %显示相位图
title(' phase spectrum');
end

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