How to generate double pendulum using ode 45

Question

Zhukun Wang 2021-2-23

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/754029-how-to-generate-double-pendulum-using-ode-45

编辑： darova 2021-2-24

function Math462hw2Q3parta 
m1=1;
m2=1;
l1=1;
l2=1;
g=9.8;
tspan=0:1:100;
%theta1initial=pi/8;
%theta2initial=pi/8;
theta1=pi/8;
theta2=pi/8;
theta1dot=0;
theta2dot=0;
thetainitial=[theta1 theta2 theta1dot theta2dot];
%Write out the ode45 function
[t,thetasoln]=ode45(@(t,thetainitial)derivativefuncs(t,thetainitial,m1,m2,l1,l2,g),tspan,thetainitial);
%Plot function
plot(t,thetasoln,'bl');
xlabel('time');
ylabel('value');
title('double pendulum');
    function dxdt=derivativefuncs(~,thetavalues,m1,m2,l1,l2,g)
        theta1=thetavalues(1);
        theta2=thetavalues(2);
        theta1dot=thetavalues(3);
        theta2dot=thetavalues(4);
        
        theta1doubledot=(m2*l2*theta2doubledot*cos(theta1-theta2)+m2*l2*theta2dot^2*sin(theta1-theta2)+(m1+m2)*g*sin(theta1))/((m1+m2)*l);
        theta2doubledot=l1*theta1doubledot*cos(theta1-theta2)-l1*theta1dot^2*sin(theta1-theta2)+g*sin(theta2);
        dxdt=[theta1doubledot;theta2doubledot];
        
    end 
end

Just got another question on how to use ode 45 to generate the double pendulum model. I think the problem is Matlab keeps saying the line with ode45 function is still wrong but there is no marks in the code. I think I did pass the parameters but it still does not work. Can some one maybe help?