fft error in function?

data_output is a 60000x2 matrix.

Concerning line the line that is highlighted with arrows, "fhat = fft(f,n);", I keep recieving "Error using fft

Invalid data type. First argument must be double, single, int8, uint8, int16, uint16, int32,uint32, or logical.".

What can I do to make the code function? Are either t or f that is the problem?

dt = .001;
t = 0:dt:1;
f = 'data_output(:1)';
figure;
plot(t,ffilt);  ",
dt = .001;
%dt = 0.00001666667;
t = 0:dt:1;
f = 'data_output(:1)';

figure;
plot(data_output)
xlabel('time(s)');
ylabel('Amplitude');
grid on

%% Compute the Fast Fourier Transform FFT
n = length(t);

 -----------------------------   >>>fhat = fft(f,n);      <<<  ------------------------
PSD = fhat.*conj(fhat)/n; 
freq = 1/(dt*n)*(0:n); 
L = 1:floor(n/2); 


figure; 
dim = 2;
plot(f,fhat,2);                         % FFT plot 
xlim([0 1]);
xlabel('Frequency(Hz)');
ylabel('FFT Magnitude'); 
grid on
%% USe the PSD to filter out noise 
indices PSD>35000; 
PSDclean = PSD.*indices;
fhat = indices.*fhat; 
ffilt = ifft(fhat); 

figure;
plot(t,ffilt);  

[KSSV]

What for is this line?

f = 'data_output(:1)';

I guess it should be

f = data_output(:,1);

Isn't it? In your case what is

class(f)

Answer 1

[Walter Roberson]

f = 'data_output(:1)';

That is a character vector. You cannot fft() a character vector.

If you need to apply fft to the ASCII codes that are used for the letters 'd' 'a' 't' and so on, then fft(double(f), n) . I would, however, suggest that it is very unlikely that is what you want, and that instead your line should be something closer to

f = data_output(:,1);

where data_output would be replaced by the name of the variable whose first column you want to extract.

plot(t,ffilt);  ",

ffilt is not defined at that point.

You have a stray double-quote on that line.

plot(f,fhat,2);                         % FFT plot 

When you use more than one numeric input to plot(), then you must have an even number of numeric inputs.

dim = 2;

That line hints that the 2 in your plot might refer to the second dimension, but your fhat looks like it will be a vector so it does not appear that giving the dimension would be useful.

If you are expecting that f or fhat are 2D arrays, then some of your other lines will have problems.

indices PSD>35000; 

There is no MATLAB function named indices to invoke on the character vector 'PSD>35000' . I would suspect

indices = PSD>35000;

[Alia Hicks]

Thanks for noticing my errors. I've started over. I get the error "Invalid expression. When calling a function or indexing a variable, use parentheses. Otherwise, check for mismatched delimiters." at the second from last line "plot(t,f,); %amp vs time"

dt = .001;
t = 0:dt:1;
f = data_output;

%%Compute the Fast Fourier Transform FFT
n = length(t);
fhat = fft(f,n);       % Compute the fast Fourier transform
PSD = fhat.*conj(fhat)/n; % Power spectrum (power per freq)
freq = 1/(dt*n)*(0:n); % Create x-axis of frequencies in Hz
L = 1:floor(n/2);   % Only plot the first half of freqs

%%Use the PSD to filter out noise
indices = PSD>100;  % Find all freqs with large power
PSDclean = PSD.*indices;  % Zero out all others
fhat = indices.*fhat;  % Zero out small Fourier coeffs. in Y
ffilt = ifft(fhat); % Inverse FFT for filtered time signal

%%PLOTS
plot(t,f,);  %amp vs time
plot(f,fft); % mag vs freq

[Walter Roberson]

plot(t,f,);  %amp vs time

Why do you have a comma right before the ) ?

Note that you do not appear to have "hold on" in effect, so your second plot() is going to erase the first plot()

[Alia Hicks]

That comma was an error. I'm using hold on now.

plot(t,f), hold on

plot (f,fft);

Error recieved, "Error using plot Vectors must be the same length. Error in Julytwentyseventh (line 21)

plot(t,f), hold on"

[Walter Roberson]

What is size(data_output) ?

Is there a reason that you are making your number of samples for your time different than the number of data points you have? I would think it more likely that you should define

n = length(data_output);
dt = 0.001;
t = (0:n-1) * dt;