When I try this code for simple pendulum, I get results:
syms pt(t) th(t)m=1; l=0.5; g=9.81;e1= diff(th)*(m*l^2)==pt;e2= diff(pt)==-m*g*l*sin(th);vars = [pt(t); th(t)];V = odeToVectorField([e1,e2]);M = matlabFunction(V, 'vars', {'t','Y'});interval = [0 5];y0 = [0; pi/4];ySol = ode45(M,interval,y0);tValues = linspace(interval(1),interval(2),1000);a= deval(ySol,tValues,1)/(m*l^2);plot(tValues,a)But when I use it for triple pendulum, it gives error. Couldn't solve it. Sorry if it's simple to figure out. Really new here.
syms theta1(t) theta2(t) theta3(t) p1(t) p2(t) p3(t)m1=1; m2=1; m3=1; l1=1; l2=1; l3=1; g=9.81; tau1=0; tau2=0; tau3=0; I1=0; I2=0; I3=0; e1= diff(theta1)*(I1+(m1+m2+m3)*l1^2)... +diff(theta2)*(m2+m3)*l1*l2*cos(theta1-theta2)+... diff(theta3)*m3*l1*l3*cos(theta1-theta3)==p1; e2= diff(theta1)*(m2+m3)*l1*l2*cos(theta1-theta2)+... diff(theta2)*(I2+(m2+m3)*l2^2)+... diff(theta3)*m3*l2*l3*cos(theta2-theta3)==p2; e3= diff(theta1)*m3*l1*l3*cos(theta1-theta3)+... diff(theta2)*m3*l2*l3*cos(theta2-theta3)+... diff(theta3)*(I3+m3*l3^2)==p3; e4= diff(p1)== tau1-tau2-(m2+m3)*diff(theta1)*diff(theta2)*sin(theta1-theta2)... -m3*diff(theta1)*diff(theta3)*l1*l3*sin(theta1-theta3)... -(m1+m2+m3)*g*l1*cos(theta1); e5= diff(p2)==tau2-tau3+(m2+m3)*diff(theta1)*theta2*l1*l2*sin(theta1-theta2)... -m3*diff(theta2)*diff(theta3)*l2*l3*sin(theta2-theta3)... -(m2+m3)*g*l2*cos(theta2); e6= diff(p3)==tau3+(m3)*diff(theta1)*diff(theta3)*l1*l3*sin(theta1-theta3)... +m3*diff(theta2)*diff(theta3)*l2*l3*sin(theta2-theta3)... -m3*g*l3*cos(theta3); vars= [theta1(t);theta2(t);theta3(t);p1(t);p2(t);p3(t)]; V = odeToVectorField([e1,e2,e3,e4,e5,e6]); M = matlabFunction(V,'vars', {'t','Y'});I have get that error in simple pendulum too, it was pt==diff(th)*(m*l^2), then I put the pt to the end, and it's solved. In triple pendulum I tried leaving diff(theta1) alone didn't work, tried to this code too, but nothing changed. Original equations are:
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