Index exceeds the number of array elements (2).

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Journi Northorp
Journi Northorp 2021-2-15
编辑： James Tursa 2021-2-16
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

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回答（1 个）

James Tursa
James Tursa 2021-2-15
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?
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Journi Northorp
Journi Northorp 2021-2-15
how would I increase the number of array elements to fit this?
James Tursa
James Tursa 2021-2-16
编辑：James Tursa 2021-2-16
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.

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