Error trying to implement a 1-D fast fourier Transform

Im trying to get a 1D fft from a signal and keep getting this error saying:

"Error using fft

Invalid data type. First argument must be double, single, int8, uint8, int16,

uint16, int32, uint32, or logical."

This is my script:

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A = 7;

P = 100;

M = 15;

t = 0:1:sym(P); % Signal duration/length

fncT = (A.^t) - floor(A.^t/M)*M;

plot(t,fncT)

title('1')

xlabel('2')

ylabel('4')

Fs = 1000; % Sampling freq

Ts = 1/Fs; % Sampling period of time step

L = length(fncT); % The length of the domain signal

sig_FFT = fft(fncT,L)/L;

amplitude = 2*abs(sig_FFT(1:L/2+1));

frequency = Fs/2*2linspace(0,1,L/L2+1);

figure;

plot(Frequency,amplitude));

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How do I solve this issue?

Answer 1

[Star Strider]

After a fair amount of editing (please proofread your code), this works:

A = 7;
P = 100;
M = 15;
t = 0:1:sym(P); % Signal duration/length
fncT = (A.^t) - floor(A.^t/M)*M;
plot(t,fncT)
title('1')
xlabel('2')
ylabel('4')

Fs = 1000;  % Sampling freq
Ts = 1/Fs;  % Sampling period of time step
L = length(fncT);    % The length of the domain signal
sig_FFT = fft(double(fncT),L)/L;
amplitude = 2*abs(sig_FFT(1:fix(L/2)+1));
frequency = Fs/2*linspace(0,1,fix(L/2)+1);
figure;
plot(frequency,amplitude);

Note the changes required for it to run with out error.

[Prayash Thapa]

Oh thank you kind sir, I did proof read it 3 times but maybe because I am to tired rn.

[Prayash Thapa]

What does fix() do?

[Star Strider]

My pleasure!

The fix function rounds its arguments toward 0, producing integer outputs. (The floor function rounds them toward -Inf, the ceil function rounds them toward +Inf, both producing integer outputs, and the round function rounds to the nearest integer, unless other arguments are included. They are all linked to in the fix documentation, so I do not specfically link to the m here.)