Can you help me to draw graph Amplitude and Frequency from code below, I lost time very much but don't it. Thank you very much.

function main
d1=1;
v=10;
t_end=100*0.5*d1/v;
t=0:0.01:t_end;
y0=[0;0;0;0];
[t,y]=ode45(@daodong,t,y0);
hold on;grid on;
plot(t,y(:,1));
xlabel('Thoi gian (s)')
ylabel('Bien Do dao dong (m)')
title('DAO DONG CUA HANH KHACH')
end
function yp = daodong(t,y)
c=10;
vt=10;
k1=84.24;
m1=5.265;
I1=0.2322;
a=0.21;
yp = zeros(4,1);
yp(1) = y(2);
yp(2) = ((-(c*(y(2)-0.05*2*pi*vt*(sin(4*pi*vt*t))-(a*y(4)/2))+k1*(y(1)-(0.05*(sin(2*pi*vt*t))^2)-(a*y(3)/2))))/m1);
yp(3) = y(4);
yp(4) = ((-(a*c*(y(2)-0.05*2*pi*vt*(sin(4*pi*vt*t))-(a*y(4)/2))+a*k1*(y(1)-(0.05*(sin(2*pi*vt*t))^2)-(a*y(3)/2))))/(2*I1));
end

[Walter Roberson]

See the first example in the documentation for fft() for how to draw a frequency graph and label it properly.

[Johnny Vendetta]

oh, nice to meet you. Thank you very much.