How to find fft for a system of two variables? Can you check my code if it is right, please?

function aaa

b= 3;

        [t,x]=ode45(@DoubleSpeciesSystem, 0:0.01:10000 , [30 6] , [] , b);

n = length(x);

h=0.01;

dt = t(end)/(n-1);

Fs=1/dt;

NFFT=n;

y=fft(x,NFFT)/n;

f=linspace(0,1,NFFT/2+1)*(Fs/4);

Pow = abs(y(1:NFFT/2 +1)).^2; % Power of the DFT

Pow(1) = 0;

figure(1) % Plot single-sided amplitude spectrum.

plot(f,Pow)

1;

%function dxdt = DoubleSpeciesSystem(t,x,b)

%x(1) = prey

% x(2) = predator

%dxdt(1) = 15 * x(1) - b * x(1).* x(2);

%dxdt(2) = -5 * x(2) + 0.5 * x(1).* x(2);

%dxdt = [dxdt(1) dxdt(2)]';

%end