ifft returns NaN when plotting the impulse response function
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Hello, I seem to be having issues using MATLAB's fft and ifft functions.
An impulse response function h(t) has the following formula: inj(t) * h(t) = AIF(t). We know that the graphs of inj(t) and AIF(t) are as followed. I wrote the following code to do the deconvolution but h(t) in the output graph is zero.
I realized that the h returns from ifft is NaN but I don't know how to correct the code. Thanks!
load("AIF_1.mat");
load("inj_1.mat");
inj_1 = inj(201:2400);
inj1_FFT = fft(inj_1);
AIF_1 = AIF(201:2400);
AIF1_FFT = fft(AIF_1);
h_FFT = AIF1_FFT ./ inj1_FFT;
h_FFT(isnan(h_FFT)==1) = 0;
h = ifft(h_FFT);
X = zeros(1,200)
ht = [X,h];
plot(time,real(ht));title('h(t)');
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Accepted Answer
Paul
on 10 Apr 2023
Hi 粤轩 杨,
It looks like h_FFT also has a few values that are inf, in addition to the NaNs
load("AIF_1.mat");
load("inj_1.mat");
inj_1 = inj(201:2400);
inj1_FFT = fft(inj_1);
AIF_1 = AIF(201:2400);
AIF1_FFT = fft(AIF_1);
h_FFT = AIF1_FFT ./ inj1_FFT;
sum(isnan(h_FFT))
sum(isinf(h_FFT))
% quick correction to get things to run, not sure if this is really what
% should be done
inj1_FFT(inj1_FFT == 0) = eps;
h_FFT = AIF1_FFT ./ inj1_FFT;
sum(isnan(h_FFT))
sum(isinf(h_FFT))
h = ifft(h_FFT);
X = zeros(1,200);
ht = [X,h];
plot(time,real(ht));title('h(t)');
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