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Solving ODEs using matlab (ode45)

Asked by Pazzo Giampalo on 19 Jul 2013
Latest activity Answered by SANDEEP KUMAR R on 14 Sep 2016
I am new to matlab. I was trying to follow an instruction from
I want to use ode45 to solve ODEs.
I have the following in my function page:
function dxy = diffxy (t, xy)
x = xy(1);
xdot = xy(2);
y = xy(3);
xdot = xdot;
ydot = 3*x+5;
xdoubledot = 3-ydot+2*xdot
dxy = [xdot; xdoubledot; ydot]
To get a solution, I type [T, XY] ode45 ('diffxy', 0, 10, [0 1 0]) in my command window (t from 0 to 10 and the initial value of x is 0, xdot is 1, and ydot is 0). But the following message :
??? [T, XY] ode45 ('diffxy', 0 10, [0 1 0])
Error: Unexpected MATLAB expression.
I wonder if anyone could please help.

  1 Comment

on 20 Jul 2013
What is "my function page"?
I've formatted your code. Please read the "? Help" link to find out, how to do this by your own. Thanks.
You need an additional "=" to assign the output.

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3 Answers

Answer by Matt Kindig on 19 Jul 2013

Did you forget the assignment sign?
[T, XY] = ode45 ('diffxy', 0 10, [0 1 0])


thank you Matt, but no, that didn't work. I guess my question is, when I have the function page written out, how do I call that function (execute it) in my command window? I tried to look up online, but still not figure it out using ode45.
on 20 Jul 2013
Please explain "didn't work" with details. And we have to know, where you have written the shown code.

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Answer by Pazzo
on 3 Aug 2013

I found out that I should add a bracket, [ ],along with an equal sign, =, to make it work.
thank you for your help though.


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Answer by SANDEEP KUMAR R on 14 Sep 2016

Instead of 'diffxy' use @diffxy in ode45


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