Solving ODE two sets of initial conditions

I have to solve the equation yp = [y(2);(-(z*y(2)+w*y(1)+beta*y(2)^3+n*y(1)^3))]; and display the results in a phase plot. How do I include initial conditions for both the displacement and the velocity? Here is my code:

function [t,y] = call_trial1()
tspan = [0 5]; % set time interval
y0 = [-1;1]; % set initial condition

[t,y] = ode15s( @trial1 ,tspan ,y0);
plot(t,y)
xlabel('Structural Displacement(m)')
ylabel('Structural Velocity(m/s)')
grid on
disp([t,y]) % displays t and y(t)
function yp = trial1 (t,y)
m=1.2; c=4; k=1600;
cf=-8; kf=100; beta=20; n=-2.5;
z=(cf-c)/m; w=(kf-k)/m;

yp = [y(2);(-(z*y(2)+w*y(1)+beta*y(2)^3+n*y(1)^3))]; 
end

end

Answer 1

[Star Strider]

I may be missing something, but it seems you already have:

y0 = [-1;1]; % set initial condition

[moonman1]

Would this not only cover one variable (in this case velocity) over a certain range. How would I add another variable? here's the type of plot im looking for:

[moonman1]

s

[Star Strider]

The initial conditions are those for the two vectors in your ODE function, whatever they are. For a typical second-order system (at least as I understand it), y(1) is the displacement, y(2) is its derivative, so the initial conditions are for y(1) and y(2) respectively.

[moonman1]

this is the equation i want to model. what is the best way to write it in matlab

[Star Strider]

I thought you already did that?