MATLAB: How to Plot a second derivative equation

Question

Hi all,

The equation I want to plot is

I've tried to gether information online and come up with the code:

clc
clear
syms x(t)
Dx = diff(x);
D2x = diff(x,2);
w = 1
dt = 1/1000;
t = 0:dt:1000*dt;
equ = D2x + (Dx)^3 + x(t)^2 *Dx + x(t) == 0;
figure
fplot(equ)

How to plot the graph with the time interval t?

Edit:

To plot the 2 equation and plot them on the same graph

Can I use the code like this:

syms x_1 x_2 equ(t) 
Dx_1 = diff(x_1);
D2x_1 = diff(x_1,2);
Dx_2 = diff(x_2);
D2x_2 = diff(x_2,2);
w_1 = w_2 = 1
a_1 = a_2 = 1
B_1 = B_2 = 1
r_1 = r_2 = 1
equ_1 = D2x_1 + (a_1*(Dx_1) + B_1*x_1^2 - r_1 )*Dx_1 + w_1^2*x_1;
equ_2 = D2x_2 + (a_2*(Dx_2) + B_2*x_2^2 - r_2 )*Dx_2 + w_2^2*x_2;
figure
fimplicit(equ_1, [-1 1]) % Use _fimplicit1 To Plot ‘equ(t)=0’
hold on
fimplicit(equ_2, [-1 1])
grid

Would the graph plot with this code be the solution of the equation?

Answer 1

Try this:

syms x(t) equ(t) 
Dx = diff(x);
D2x = diff(x,2);
w = 1
% dt = 1/1000;
% t = 0:dt:1000*dt;                                     % Not needed Here
equ = D2x + (Dx)^3 + x(t)^2 *Dx + x(t);
equ(t) = subs(equ, x, {exp(-1i*w*t)+exp(1i*w*t)})       % Substitute Expression For 
figure
fimplicit(equ, [-1 1])                                  % Use ‘fimplicit’ To Plot ‘equ(t)=0’
grid

The plot is absolutely not interesting, however the code runs without error!