solve IVP with ode45
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So I am trying to generate an ODE45 graph with the file provided. I made the modification which I believe are correct but the graph generated at the output is not correct. The second function
function dYdt=f(x,Y)
has a modified version of my function and I am wondering if that is causing the ODE function not to generate the proper input. Would anyone be able to advise on a solution or where I am going wrong ?
Thank you
采纳的回答
Alan Stevens
2020-7-28
Looks like your equation is not correct for non-linear pendulum! Try the following:
% If u = angle from vertical then d^2u/dt^2 = -(g/l)sin(u)
%
% Let v = du/dt; dv/dt = -(g/l)sin(u);
Y0 = [1 2];
tspan = 0:0.1:10;
ge = 32; % Earth
[t, Y] = ode45(@f, tspan, Y0, [], ge);
ue = Y(:,1);
gm = 0.165*ge;
[t, Y] = ode45(@f, tspan, Y0, [], gm);
um = Y(:,1);
plot(t, ue, t, um), grid
xlabel('time'), ylabel('angle')
legend('Earth','Moon')
function dYdt = f(~,Y,g)
l = 3;
u = Y(1);
v = Y(2);
dudt = v;
dvdt = -g/l *sin(u);
dYdt = [dudt; dvdt];
end
更多回答（1 个）
sawera
2025-8-6
0 个投票
find exact solution of IVPs, then compute using approximate solution at x=0:0.2.2:2 using ode45 command
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