phase plane in MATLAB?

Hi I have a equations here, and I wonder it to do phase plane.How to do it?

Answer 1

[Mischa Kim]

Hello, check out the code below:

function my_ODE()
th0     = 0;
Dth0    = 1;

tspan   = linspace(0,2,200);
options = odeset('RelTol',1e-8,'AbsTol',1e-10);

[~,X]   = ode45(@DE, tspan,[th0; Dth0],options);
plot(X(:,1),X(:,2))
grid
end

function dX = DE(~,x)
dX = [x(2); u(x(1))];
end
function uval = u(x1)
if (x1 < 0)
    uval = +5;
else
    uval = -5;
end
end

[JIE YUANG LU]

so when I change U condition which code to change? and what is DE?