warning off MATLAB:polyfit:RepeatedPointsOrRescale

damper1=Monturn2;               % assign displacement data to Matlab vector
damper2=LBturn4;
Fs=200;                         % sampling frequency

n1=length(damper1);             % Data from Pi Toolbox has time and distance
x1=damper1(n1+1:200/Fs:end);    % Only getting distance data
n1=length(x1);
t1=[0:1/Fs:(n1-1)/Fs];          % Make a separate time vector

n2=length(damper2);
x2=damper2(n2+1:200/Fs:end);
n2=length(x2);
t2=[0:1/Fs:(n2-1)/Fs];

figure(1)                       % Graph displacements of the two dampers
plot(t1,x1,'-b',t2,x2,'-r')
xlabel('time [s]')
ylabel('displacement [in]')
legend('Montreal turn 2 (road)','Long Beach turn 4 (street)')
title('Damper Displacement')
grid;

t1=(0:n1-1)/Fs;                 % Re-assign time vector
p1=abs(fft(x1))*2/(n1);         % Absolute value of the FFT divided by N/2
p1=p1-p1(round(n1/2));          % Subtraction to account for voltage offset
p1(1)=p1(1)/2;                  
f1=(0:n1-1)*(Fs/n1);            % Frequency vector (in Hz)

t2=(0:n2-1)/Fs;
p2=abs(fft(x2))*2/(n2);
p2=p2-p2(round(n2/2));
p2(1)=p2(1)/2;
f2=(0:n2-1)*(Fs/n2);

[P1,S1]=polyfit(f1(round(n1/13):round(n1/1.5)),p1(round(n1/13):round(n1/1.5)),7);
fit1=polyval(P1,f1);            % Best fit polynomial to the frequency data

[P2,S2]=polyfit(f2(round(n2/13):round(n2/1.5)),p2(round(n2/13):round(n2/1.5)),7);
fit2=polyval(P2,f2);

figure(2)                       % Graph the Fourier Transform
plot(f1,p1,'-b',f2,p2,'--r')
xlabel('Frequency [Hz]')
ylabel('Amplitude [in]')
legend('Montreal turn 2 (road)','Long Beach turn 4 (street)')
title('Frequency Distribution')
axis([15 100 0 0.003])
grid;

figure(3)
plot(f1,fit1,'-b',f2,fit2,'--r')
xlabel('Frequency [Hz]')
ylabel('Amplitude [in]')
legend('Montreal turn 2 (road)','Long Beach turn 4 (street)')
title('Frequency Distribution (Best Fit line)')
axis([15 100 0 0.003])
grid;