MATLAB: I need to get the maximum amplitude in this code but the final answer is wrong

fft

The data file
https://www.dropbox.com/s/8b8u38ghve7tfv0/Data.mat?dl=0
i get 28400 as the answer but the answer is wrong plus the question want its to 1 dp so i am fairly certain my code is wrong please help
load('data.mat');
dt=t(2)-t(1);% t vector has equally spaced t so this seprates t values
N=length(t);
F=fft(f,N); %fast fourier transform of f/N
Fshifted=fftshift(F);%place 0 frequency in the centre
Fmag=abs(Fshifted);%magnitude of fshifted 
nu_NY=(1/dt)/2;%nquist frequency 
nu=linspace(0,nu_NY,N/2+1);%spectrum of frequncy vals associated with FFT frequencies 
%adding postive and negative frequncies 
F1=Fmag((N/2)+1:N);
F2=Fmag(N/2:-1:1);
a=[F1,0]+[0,F2];
%plotting amplitued vs assoicated frequencies
plot(nu,a)

Best Answer

‘i am fairly certain my code is wrong’
So am I.
Try this: 
D = load('Data.mat');
f = D.f;
t = D.t;
dt=t(2)-t(1);% t vector has equally spaced t so this seprates t values
N=numel(t);
F=fft(f)/N; %fast fourier transform of f/N
Fshifted=fftshift(F);%place 0 frequency in the centre
Fmag=abs(Fshifted);%magnitude of fshifted 
nu_NY=(1/dt)/2;%nquist frequency 
nu=linspace(-nu_NY,nu_NY,N);%spectrum of frequncy vals associated with FFT frequencies 
%adding postive and negative frequncies 
F1=Fmag((N/2)+1:N);
F2=Fmag(N/2:-1:1);
% a=[F1,0]+[0,F2];
%plotting amplitued vs assoicated frequencies
plot(nu,abs(Fshifted)*2)
[pks,locs] = findpeaks(abs(Fshifted)*2, 'MinPeakHeight',10);
fprintf(1,'Peak Frequencies & Amplitudes:\n\tFrequency\tAmplitude\n')
fprintf(1,'\t%8.4f\t%8.4f\n', [nu(locs); pks])
producing: 
Peak Frequencies & Amplitudes:
	Frequency	Amplitude
	 -7.9790	 14.2000
	  8.0290	 14.2000
My changes are primarily with respect to ‘nu’, although I also correctly scaled the result of your fft call. I added a call to findpeaks (link). (I did not delete parts of your code that I believe to be irrelevant to what you want to do.)
Related Question