Unexpected output when trying to plot the solution to a system of nonlinear differential equations

Question

Aleem Andrew 2020-4-3

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/515194-unexpected-output-when-trying-to-plot-the-solution-to-a-system-of-nonlinear-differential-equations

评论： Aleem Andrew 2020-4-4

The following Matlab code is meant to plot x(1) vs time and x(2) vs time separately, but only plots x(1) vs time. Despite there being two lines of code to generate each plot, one line is ignored. Does anyone have any suggestions as to how the code can be modified?

t = [0 10]; %time interval ranges from 0 to 10 s 
ic = [pi/3; 0; 0; 0]; % initial conditions = [θ θ' x x'] 
[t,x] = ode45(ode, t, ic);
plot(t,x(:,1), 'o') %the y axis represents 
plot( t,x(:,2),'o') %the y axis represents 
xlabel('x(m)');
ylabel('θ(rad)');
function dydx = fun(t,x)
%[x(1) x(2) x(3) x(4)] = [angle angular velocity x position x velocity] respectively 
    L = 0.5; g = 9.81;  
    dydx = zeros(4,1);
    dydx(1) = x(2);
    dydx(2) = (4*sin(x(1))*(5*L*cos(x(1))*x(2)^2 + 6*g))/(L*(20*cos(x(1))^2 - 23));
    dydx(3) = x(4);
    dydx(4) = -(5*sin(x(1))*(23*L*x(2)^2 + 24*g*cos(x(1))))/(6*(20*cos(x(1))^2 - 23));
end