Graph is Blank ? why?

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Alia Hicks
Alia Hicks am 13 Aug. 2020
Kommentiert: Walter Roberson am 13 Aug. 2020
The graph for Magnitude vs Frequency is blank. Why is that? The graph of time vs ich isn't blank. y_fft is a 4001x1 column with each entry being Nan. I do not understand why
load AdaptiveFiltereData
d = AdaptiveFilteredData;
fs =100;
dt = .001;
t = 0:dt:4.0001;
%ich = AdaptiveFilteredData.ichannel;
%qch = AdaptiveFilteredData.qchannel;
%plot(ich,qch);
%%PLOTS
%plot(t,ich);
%plot(t,qch);
figure;
plot(t,ich)
xlabel('time(s)');
ylabel('Amplitude');
grid on
Nsamps = length(ich); % Window length
y_fft = abs(fft(ich)); %Retain Magnitude
%f = fs(1/(dt*n)*(0:n));
f = fs*(0:Nsamps/2-1)/Nsamps; %Prepare freq data for plot
figure;
plot(f, y_fft(1:length(f)));
%Magnitude vs Freplot(f, y_fft); % FFT plot
xlim([0 1]);
xlabel('Frequency(Hz)');
ylabel('FFT Magnitude');
grid on
  1 Kommentar
hosein Javan
hosein Javan am 13 Aug. 2020
can you share the image of plot(t,ich) or its data file?

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Antworten (2)

Walter Roberson
Walter Roberson am 13 Aug. 2020
"The graph of time vs ich isn't blank"
At least one entry in ich is nan or infinite, and that is leading to the fft being all nan. fft can only process finite points.
Another possibility is that the individual points are all finite but that they are large enough that the fft calculations are overflowing. For example if the values exceed sqrt(realmax) then multiplication could create infinity
  4 Kommentare
hosein Javan
hosein Javan am 13 Aug. 2020
Bearbeitet: hosein Javan am 13 Aug. 2020
Walter Roberson thank you for replying. I've seen it before. I wonder how someone has managed to do something with matlab with its limitation of realmax.if it says it is not symbolic. is it using strings to compute these large data? or is it below realmax but can show more digits? another thing. what about speed? is it as slow as symbolic toolbox? because however matlabbuiltin functions are written in C language.
Walter Roberson
Walter Roberson am 13 Aug. 2020
If you are talking about John's contributions then the answer is that he defined a class and operations on the class. The class uses blocks of numbers as decimal digits, and standard techniques for extended precision calculations.

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Bruno Luong
Bruno Luong am 13 Aug. 2020
Bearbeitet: Bruno Luong am 13 Aug. 2020
Try to add this after the statement of loading the file
ich=fillmissing(ich,'nearest')
and see it it fixes the issue.

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