ifft returns NaN when plotting the impulse response function

13 次查看（过去 30 天）
粤轩 杨
粤轩 杨 2023-4-10
评论： 粤轩 杨 2023-4-10
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)');

请先登录，再回答此问题。

采纳的回答

Paul
Paul 2023-4-10
Ran in:
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))
ans = 3
sum(isinf(h_FFT))
ans = 2
% 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))
ans = 0
sum(isinf(h_FFT))
ans = 0
h = ifft(h_FFT);
X = zeros(1,200);
ht = [X,h];
plot(time,real(ht));title('h(t)');
  1 个评论
粤轩 杨
粤轩 杨 2023-4-10
Hi Paul,
The output graph is a little strange. But you finging of inf values in h_FFT made me realize that I didn't intercept the inj correctly.
After changing to
inj_1 = inj(200:2400)
the output graph is good!
Thank you for your inspiration!

请先登录，再进行评论。

更多回答（1 个）

粤轩 杨
粤轩 杨 2023-4-10
There are two related attachments for your information. Thanks!
  1 个评论
粤轩 杨
粤轩 杨 2023-4-10
Just as mentioned above, the final code should be
load("AIF_1.mat");
load("inj_1.mat");
inj_1 = inj(200:2400);
inj1_FFT = fft(inj_1);
AIF_1 = AIF(200:2400);
AIF1_FFT = fft(AIF_1);
h_FFT = AIF1_FFT ./ inj1_FFT;
h = ifft(h_FFT);
X = zeros(1,199);
ht = [X,h];
plot(time,real(ht));title('h(t)');
And the output graph looks like

请先登录，再进行评论。

类别

在 Help Center 和 File Exchange 中查找有关 Transforms 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by