ODE45 for a second order differential equation

2018 4 21
3 个回答
回答已采纳
更新时间：2021 6 30
186 次查看（30 天）

1 个投票

I have a second order differential equation : y''=(2*y)+(8*x)*(9-x); Boundary Conditions y(0)=0 , y(9)=0 Need to solve the diff eq using ode45.
I've tried watching a bunch of tutorials but I just cannot seem to figure out how the function is written as a column vector [y';y'']. I don't understand it at all and that might make this query vague too.
Hope someone can help with the code or the explanation on how to solve the above.
Thank you

请先登录，再回答此问题。

 采纳的回答

Torsten
Torsten 2018-4-23

3 个投票

[x,y] = ode45(@fun,[0 9],[0 -28]);
function dy = fun(x,y)
dy = zeros(2,1);
dy(1) = y(2);
dy(2) = 2*y(1)+8*x*(9-x);
But for a boundary value problem like yours, you will have to use "bvp4c" instead of "ode45".
Best wishes
Torsten.

5 个评论
显示 3更早的评论 隐藏 3更早的评论

Remston Martis
Remston Martis 2018-4-23
编辑：Remston Martis 2018-4-23

Error :

>> [x,y] = ode45(@fun,[0 9],[0 -28]);
Attempt to execute SCRIPT ode45 as a function:
C:\Users\remst\Desktop\ode45.m

using bvp4c says too many input arguments.

Torsten
Torsten 2018-4-23

Put

function main
[x,y] = ode45(@fun,[0 9],[0 -28]);

function dy = fun(x,y)
dy = zeros(2,1);
dy(1) = y(2);
dy(2) = 2*y(1)+8*x*(9-x);

in one file, name it main.m and execute it as a function file.

Best wishes

Torsten.

Remston Martis
Remston Martis 2018-4-23
编辑：Remston Martis 2018-4-23
Just doesn't seem to work .
Error Message: Attempt to execute SCRIPT ode45 as a function: C:\Users\remst\Desktop\ode45.m
Error in main (line 2) [x,y] = ode45(@fun,[0 9],[0 -28]);
I tried running the script and I tried calling the function in the commany window. Gives me the same error.
Torsten
Torsten 2018-4-23
编辑：Torsten 2018-4-23
There seems to be a duplicate of ode45 on your desktop - rename or remove it.
Remston Martis
Remston Martis 2018-4-23
Brilliant. Thank you Torsten!

请先登录，再进行评论。

更多回答（2 个）

Stephan
Stephan 2018-4-22
编辑：Stephan 2018-4-22

1 个投票

Hi,

transform a n-th order ode into a system of n 1st order ode's to solve it.

Matlab documentation example: https://de.mathworks.com/help/matlab/math/solve-nonstiff-odes.html

More examples here: https://www.google.de/url?sa=t&source=web&rct=j&url=http://www.math.poly.edu/courses/ma2132/Notes/MA2132EquationsToSystems.pdf&ved=2ahUKEwiQ_tCRq83aAhWMMewKHQ7CC1IQFjALegQIBxAB&usg=AOvVaw07Im9F42d9LrfvRIzL35Pd

If you read this i guess you can quickly solve your problem.

2 个评论
显示 无 隐藏 无

Remston Martis
Remston Martis 2018-4-23
编辑：Remston Martis 2018-4-23

I keep getting these errors: Attempt to execute SCRIPT ode45 as a

function: C:\Users\remst\Desktop\ode45.m

Error in ode45 (line 3) [x,y] = ode45(@fun,[0 9],[0 -28]);

My function declarations are:

function fun=fun(x,y)
fun=zeroes(2,1);
fun(1)=y(2);
fun(2)=(2*y(1))+8*x*(9-x);

Calling the function :

[x,y] = ode45(@fun,[0 9],[0 -28]);

Where am I going wrong? I've tried 10000s of ways

Ebraheem Menda
Ebraheem Menda 2021-6-30
编辑：Ebraheem Menda 2021-6-30
In this case you have declared the name of the function and its output both with the same name 'fun'. That is the problem it seems.

请先登录，再进行评论。

NARSIRAM GURJAR
NARSIRAM GURJAR 2019-9-16

0 个投票

C:\Users\remst\Desktop\ode45.m
save this file with different name

类别

在 帮助中心 和 File Exchange 中查找有关 Ordinary Differential Equations 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