The example from internet doesn't work in matlab (ODE45 for solving equation system)

Question

Tomas 2014-8-20

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/151693-the-example-from-internet-doesn-t-work-in-matlab-ode45-for-solving-equation-system

编辑： Andrew Reibold 2014-8-20

Im new on matlab, and ill trying learn how to solve some equation systems using matlab, and ode45 solver. I was tried to use a sample from matlab help, and it works great, but when im trying to solve a little bit difficult equations i get the error. its happen with all my tried was the same ( i have a six motion equation system with 6 variables, so i need to leart how to solve it using matlab) I find some example on internet and try to solve and test it on my computer, but it doesn't work, i get some error:

          >> [T, XY] ode45('diffxy',0,10,[0 1 0])
       [T, XY] ode45('diffxy',0,10,[0 1 0])
               |
      Error: Unexpected MATLAB expression.

Can someone help for me?

Source of full code and description ill find on: http://www.mit.edu/people/abbe/matlab/ode.html

What is wrong here, what i need to change for the correct result, and what is the mistake explanation?

the *.m code:

function dxy = diffxy(t, xy)
%
%split xy into variables in our equations
%
x = xy(1);
xdot = xy(2);
y = xy(3);
%
% define the derivatives of these variables from equations
%
xdot = xdot;
ydot = 3*x + 2*y + 5;
xdoubledot = 3 - ydot + 2*xdot;
%
%return the derivatives in dxy in the right order
%
dxy = [xdot; xdoubledot; ydot]

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Answer 1

Andrew Reibold 2014-8-20

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/151693-the-example-from-internet-doesn-t-work-in-matlab-ode45-for-solving-equation-system#answer_149290

编辑：Andrew Reibold 2014-8-20

在 MATLAB Online 中打开

When you called it you left out an equals sign, to start.

[T, XY] ode45('diffxy',0,10,[0 1 0]) %from this
[T, XY] = ode45('diffxy',0,10,[0 1 0]) %to this

The unrecognized expression error occurs right at the first character after where the equal sign should have been.

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Tomas 2014-8-20

Dear Andrew Reibold thank You for help, it was stupid mistake... You have eagle eyes. I get the results, now i'm going to solve my six equation system. Thank You again.

Andrew Reibold 2014-8-20

编辑：Andrew Reibold 2014-8-20

When you are working on code it can be easy to make simple mistakes like that, I know that I do things like that all the time. Good luck with your system, glad I could be of use.

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