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

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Aleem Andrew
Aleem Andrew on 3 Apr 2020
Commented: Aleem Andrew on 4 Apr 2020
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
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));

Accepted Answer

Torsten on 4 Apr 2020
hold on
between the two plot commands.

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