Problem when solving ODEs with ode45
3 次查看(过去 30 天)
显示 更早的评论
Good day,
I have the following code where I simultaneously solve three second-order differential equations defined in 'ode3'.
My problem is that in the second last line in 'ode3', the denominator is Y3(3). This is the variable 'r' and is in the direction of a spring and stretches as a mass swings around at its endpoint. When I run the script I get NaN in my Y3 matrix, which then leads me to believe I'm dividing by zero some time. What I don't understand is why would that value become zero?
Any help is appreciated!
m1 = 4; %kg
m2 = 6; %kg
L = 1.5; %m
k = 100; %N/m
g = 9.81; %m/s2
% --------------------------------------------------------------
% Force parameters
% --------------------------------------------------------------
Fo = 100; %N
tf = 1;
F = @(t) (t<=tf)*Fo*sin(2*pi*t/tf);
ic3 = [0, 0, 0, 0, L, 0];
ode3 = @(t, Y3) [Y3(4);
Y3(5);
Y3(6);
(F(t) - m2*k*(L-Y3(3))*sin(Y3(2)))/m1;
(-F(t)*cos(Y3(2)) + m2*k*(L-Y3(3))*sin(Y3(2))*cos(Y3(2)) - 2*m1*Y3(6)*Y3(5) - m1*g*sin(Y3(2)))/(m1*Y3(3));
(-F(t)*sin(Y3(2)) + m2*k*(L-Y3(3))*sin(Y3(2))^2 + m1*Y3(3)*Y3(5)^2 + m1*g*cos(Y3(2)) + m1*k*(L-Y3(3)))/m1];
[t3, Y3] = ode45(ode3, [0, 3], ic3);
0 个评论
采纳的回答
Ameer Hamza
2020-4-28
In your initial condition, you have
ic3 = [0, 0, 0, 0, L, 0];
which implies that at initial point, Y(3) = 0. But in this equation
(-F(t)*cos(Y3(2)) + m2*k*(L-Y3(3))*sin(Y3(2))*cos(Y3(2)) - 2*m1*Y3(6)*Y3(5) - m1*g*sin(Y3(2)))/(m1*Y3(3))
m1*Y3(3) comes in the denominator. At the initial point, you get a 0/0 situation. If you try some other initial condition, say
ic3 = [0, 0, 1, 0, L, 0];
You will get a finite answer.
You will need to check you system of ODE, if it is correctly written, and which value of initial conditions are allowed.
更多回答(0 个)
另请参阅
类别
在 Help Center 和 File Exchange 中查找有关 Ordinary Differential Equations 的更多信息
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!