[問題] 找不出 FFT 的錯誤已回收

看板MATLAB作者cosomyr (GT)時間17年前 (2008/12/13 06:59)推噓0(0推 0噓 0→)

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老師說,這串code有錯可是我實在找不出來錯在哪裡 (問題一) 還必須要口頭解釋畫出來的兩個圖到底在model 什麼(問題二) 我嘗試著用註解解釋了一些,但是還不是很確定希望有人能就這兩個問題提供比較明確且詳盡的解答謝謝我花了五個小時在弄這個可是還是不知道再半天就要交了... 感覺已經走投無路了哭哭真的希望有人能協助我 @@ function mysteryfunction f0 = 261.625; %frequency of the wave harm = 3.*f0; %the harmonic is in 3 times of the fequency npts = 8192; %2^13; it's a power of 2 freq = linspace(-1e4,1e4,npts); cspect = zeros(size(freq)); %generate a series of 0 %10 = bandwidth; %compute the harmonic in both positive side and negative side lv = (abs(freq - f0)<10)|(abs(freq+f0)<10); lv2 = (abs(freq - harm)<10)|(abs(freq+harm)<10); cspect(lv) = 1; %define the amplitude of a specific frequency shows on the plot cspect(lv2) = 0.25; %define the amplitude of the harmonic shows on the plot ctime = fftshift(fft(fftshift(cspect))); %fourier transform using FFT %tt = ((-npts./2):((npts./2)-1))./2e4; %frequency span = 2e4 tt = linspace(0,npts./2e4,npts); %time period figure subplot(2,1,1) plot(freq,cspect,'-r') %shows where the two harmonics located (v.s frequency) subplot(2,1,2) plot(tt,real(ctime),'-r') %plot the undulation xlim([-.02 .02]) -- ※ 發信站: 批踢踢實業坊(ptt.cc) ◆ From: 128.151.87.122