ode45 for solution of 4 dof problem

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deltanabla 2015-1-29

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https://ww2.mathworks.cn/matlabcentral/answers/173259-ode45-for-solution-of-4-dof-problem

评论： Torsten 2015-1-30

Hi Folks,

I have made up this code in an attempt to find the response time a 4 dof problem. However, I do not get an oscillatory response as I expect, instead I get a straight line which drops off towards the end. Not sure what is happening..any ideas..?

function f = Simple_Planetary(t,y)
f = zeros(8, 1);
f(1) = y(2);
f(2) = -y(7)+2*y(1);
f(3) = y(4);
f(4) = -y(7)+2*y(3);
f(5) = y(6);
f(6) = -y(7)+2*y(5);
f(7) = y(8);
f(8) = 3*y(7)-y(1)-y(2)-y(3)+10*cos(t);
y0 = [1;1;1;1;1;1;1;1];
[t,y] = ode45('Simple_Planetary', tspan, y0);
subplot (211)
plot (t,y (:, 1));
xlabel ('t');
ylabel ('x1 (t)');
subplot (212)
plot (t,y (:, 3));
xlabel ('t');
ylabel ('x2 (t)');