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S变换
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% the s-tranform test script
len = 127;
freq = 5;
t = 0:len-1;
% CREATE the chirp example
chirp = cos(2*pi*(10+t/7).*t/len);
% add a single peak in the spectrum
chirp = chirp + cos(2*pi*(10).*t/len);
[st_matrix_chirp,st_times,st_frequencies] = st(chirp);
% subplot(2,1,1);
% plot(chirp);
% subplot(2,1,2);
% contourf(st_times,st_frequencies,abs(st_matrix_chirp));
% calculate the spectrum for comparison
spe = fft(chirp);
posspe = spe(1:65);
% calculate the inverse ST
% step one: collapse over time to create the complex valued spectrum
st = st_matrix_chirp;
[ts] = inverse_st(st);
% plot out stuff
nrows = 6;
subplot(nrows,1,1);
plot(chirp);
title('chirp');
subplot(nrows,1,2);
plot(angle(spe));
title('full fft spe');
subplot(nrows,1,3);
plot(angle(fullstspe));
title('st full spe');
subplot(nrows,1,4);
plot(abs(spe - fullstspe));
title('abs of difference');
subplot(nrows,1,5);
plot(ts);
title('inverse ST time series');
subplot(nrows,1,6);
plot(ts - chirp);
title('difference between chirp and inverse ST time series (< 10-15 in magnitude)');
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