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

So I am trying to understand fast fourier transformation on matlab but when I use Y=fft(y) comand I take the invalid data type error and I have no idea neither why I am taking that error or how do solve it?

syms t
A = 2;
w = 2*pi;
phi = 5;
T = (2*pi)/w % fundamental period
y = A*sin(w*t + phi)
fplot(y, [0 3]);

title('Simulation of harmonic function');
xlabel('t[s]');
ylabel('U[mV]');

%mean value
mean_value = (1/T)*int(y,t,0,T)
%power
syms T
temp = 1/(2*T)*int(y^2,-T,T);
power = limit(temp,T, inf)
%energy
temp = int(y^2,-T,T);
energy = limit(temp,T, inf)

%Fast Fourier Tranform
Y = fft(y)

Answer 1

[Star Strider]

Since ‘y’ is a symbolic expression, it is not an appropirate argument for fft.

However, all is not lost! First, get the ‘x’ and ‘y’ data from the fplot call:

hfp = fplot(y, [0 3]);
xv = hfp.XData;
yv = hfp.YData;

then call fft with ‘yv’:

Y = fft(yv);

and the code runs as expected.

[Onur Dikilitas]

Thank you, I think I understand.

[Star Strider]

As always, my pleasure!

[Onur Dikilitas]

Okey clearly something is wrong because when I run the code with changes first I thought it works as expected. But when I add plot(Y) at the end I get this figure and it is not look like fft of sine signal.

[Star Strider]

The output of fft is a symmetrical complex vector.

Try this:

%Fast Fourier Tranform
Ts = 1/mean(diff(xv));                              % Sampling Interval
Fs = 1/Ts;                                          % Sampling Frequency
Fn = Fs/2;                                          % Nyquist Frequency
L = numel(xv);                                      % Signal Length
Y = fft(yv)/L;                                      % Fouriet Transform (Normalised)
Fv = linspace(0, 1, fix(L/2)+1)*Fn;                 % Frequency Vector
Iv = 1:numel(Fv);                                   % Index Vector

figure
plot(Fv, abs(Y(Iv))*2)
grid
xlabel('Frequency')
ylabel('Amplitude')
xlim([0 1.5]*1E-3)                                   % Optional

That should do what you want.