Question on how to use Forward Euler to simulate double pendulum

m1=1;

m2=1;

l1=1;

l2=1;

g=9.8;

dt=0.1;

theta1=[pi/8];

theta2=[pi/8];

theta1dot=[0];

theta2dot=[0];

%We can define theta1dot as w and wdot as theta1doubledot.

for t=0:dt:100-dt

theta1next=theta1(end)+dt*(theta1dot(end));

theta1dotnext=theta1dot(end)+dt*(((-m2*l2*theta2dot(end)^2*sin(theta1(end)-theta2(end))-(m1+m2)*g*sin(theta1(end)))-m2*l2*cos(theta1(end)-theta2(end))*((l1*theta1dot(end)^2*sin(theta1(end)-theta2(end))-g*sin(theta2(end)))/(l2-(m2*l2*cos(theta1(end)-theta2(end))*l1*cos(theta1(end)-theta2(end)))/((m1+m2)*l1)))));

theta2next=theta2(end)+dt*(theta2dot(end));

theta2dotnext=theta2dot(end)+dt*((l1*theta1dot(end)^2*sin(theta1(end)-theta2(end))-g*sin(theta2(end)))/(l2-(m2*l2*cos(theta1(end)-theta2(end))*l1*cos(theta1(end)-theta2(end)))/((m1+m2)*l1)));

theta1=[theta1,theta1next];

theta1dot=[theta1dot,theta1dotnext];

theta2=[theta2,theta2next];

theta2dot=[theta2dot,theta2dotnext];

end

plot(theta1,theta2);

Above is my code for simulate double pendulum using matlab. However, I do not get expected results. Could someone help me figure our what might be wrong?

Answer 1

[Dongyue]

Hi Zhukun,

The following links will show you some examples of how to use MATLAB to simulate the double pendulum motion. Please go through these links to see detailed information and coding:

https://www.mathworks.com/help/symbolic/animation-and-solution-of-double-pendulum.html

https://www.mathworks.com/matlabcentral/fileexchange/28490-double-pendulum

Best,

Dongyue