i have problem with cartesian coordinates pendulum EOM in matlab

Question

I made my code like this,

function DK = pendulum_cartesian(t,K)    
g = 9.8; l = sqrt(K(1)^2 + K(2)^2);  
DK = zeros(4,1);
DK(1) = K(3);
DK(2) = K(4);
DK(3) = ( (-K(1)*K(3)^2) - (K(1)*K(4)^2) + K(1)*K(2)*g )/(l^2);
DK(4) = ( (-K(2)*K(3)^2) - (K(2)*K(4)^2) - (K(1)^2)*g )/(l^2);

theta = atan(K(2)/K(1));

plot(t,theta);

end

and i typed,

[t,K] = ode45(@pendulum_cartesian, [0,10], [0.1,0.00017,0.1,0])

but there is no value in theta, and plots nothing.

where is a problem?

The fact that you're not getting an output suggests this is a coding problem, not an engineering numerical methods problem. I would suggest a different forum, coding help is off-topic here. — BarbalatsDilemma, Apr 22 '17 at 18:16

score 0 · Accepted Answer · answered Apr 22 '17 at 17:31

Assuming your equations and your code is correct.

This is what I used for the function:

function DK = pendulum_cartesian(t,K)    
DK = zeros(4,1);
DK(1) = K(3);
DK(2) = K(4);
DK(3) = ( (-K(1)*K(3)^2) - (K(1)*K(4)^2) + K(1)*K(2)*9.81 )/(K(1)^2 + K(2)^2);
DK(4) = ( (-K(2)*K(3)^2) - (K(2)*K(4)^2) - (K(1)^2)*9.81 )/(K(1)^2 + K(2)^2);
end

Then run with:

[t,K] = ode45(@pendulum_cartesian, [0,10], [0.1;0.00017;0.1;0]);
theta = atan(K(:,2)/K(:,1));
plot(t,theta);

i have problem with cartesian coordinates pendulum EOM in matlab

1 Answers1