清空筛选条件
清空筛选条件

Trying to solve and plot the non-linear pendulum equation

3 次查看（过去 30 天）
Alexandros
Alexandros 2017-11-16
评论： Star Strider 2017-11-17
Hi! I have the d^2/dt^2 + g/L(sinθ)=0 2nd order D.E. (Simple Pendulum) which I have seperated to two 1st order D.E.
y(1) = dθ/dt = ω = u_θ , y(2) = dω/dt = -b^2*sinθ (where b = sqrt(g/L))
I want to use ode45 to solve these equations.
I tried following the link: https://www.mathworks.com/help/matlab/ref/ode45.html but I got errors on my code.
m-file
function dydt = spendn(t,y)
dydt = [u; -sinu];
In command window:
[t,y] = ode45(@spendn,[0 7],[0; 1.57]);
I am doing something wrong here, pls help.
  1 个评论
Jan
Jan 2017-11-16
编辑：Jan 2017-11-16
Please post the complete error message.
The conversion from
y(1) = dθ/dt = ω = u_θ
y(2) = dω/dt = -b^2*sinθ (where b = sqrt(g/L))
to
dydt = [u; -sinu];
seems to be too rough. Neither "u" not "sinu" are defined.

请先登录，再进行评论。

请先登录，再回答此问题。

回答（1 个）

Star Strider
Star Strider 2017-11-16
Try this:
dydt = [u; -sin(u)];
  4 个评论
显示 2更早的评论
Alexandros
Alexandros 2017-11-17
Now I get this error:
Error using odearguments (line 92)
SPENDN returns a vector of length 4,
but the length of initial conditions vector is 2. The
vector returned by SPENDN and the initial conditions
vector must have the same number of
elements.
Error in ode45 (line 113)
[neq, tspan, ntspan, next, t0, tfinal, tdir, y0, f0, odeArgs, odeFcn, ...
Star Strider
Star Strider 2017-11-17
Use this:
function dudt = spendn(t,u)
dydt = [u(2); -sin(u(1))];
end
or this:
spendn = @(t,u) [u(2); -sin(u(1))];
Either of these will work.

请先登录，再进行评论。

类别

在 Help Center 和 File Exchange 中查找有关 Programming 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by