Index exceeds the number of array elements (2).

function vibration_ode45(m,k,c,uG,t,u0)

% m = mass

% k = spring constant

% c = damper

% uG = force of gravity

% t = time

% u0 is the initial conditions

[T,Y] = ode45(@vibration,[0,t],u0);

function[dydt] = vibration(t,y)

m = 30000;

k = 10800;

c = 200000;

uG = sin(10*t);

% initialize

dydt = zeros(2,1);

% set of 1st order ODEs

dydt(1) = y(2);

dydt(2) = (2*k*uG-4*c*y(2)-2*c(y(2)-y(4))-2*k*y(1)-k*(y(1)-y(3)))/(2*m);

end

figure(1)

plot(T,Y(:,1),'b-',T,Y(:,2),'g-.')

xlabel('time')

ylabel('\theta')

figure(2)

plot(Y(:,1),Y(:,2),'-')

xlabel('\theta')

ylabel('d\theta/dt')

end

Answer 1

[James Tursa]

This line has y(3)

dydt(2) = (2*k*uG-4*c*y(2)-2*c(y(2)-y(4))-2*k*y(1)-k*(y(1)-y(3)))/(2*m);

What is the differential equation you are solving? What is the initial condition you are feeding ode45?

[Journi Northorp]

yes, but I do not know how to debug this. The initial condition is u0.

[Journi Northorp]

how would I increase the number of array elements to fit this?

[James Tursa]

Yes, of course I can see that u0 is your initial condition, but you don't show us what u0 is. If it is a 2-element vector then y(3) will give you an indexing error. And you still haven't shown us the differential equation you are trying to solve.