## Solving ODEs using matlab (ode45)

### Pazzo Giampalo (view profile)

on 19 Jul 2013

Hello,

I am new to matlab. I was trying to follow an instruction from mit.edu.

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.
```

Thankyou!

Pazzo

Jan Simon

### Jan Simon (view profile)

on 20 Jul 2013

What is "my function page"?

You need an additional "=" to assign the output.

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### Matt Kindig (view profile)

on 19 Jul 2013

Did you forget the assignment sign?

```[T, XY] = ode45 ('diffxy', 0 10, [0 1 0])
```

Pazzo Giampalo

### Pazzo Giampalo (view profile)

on 20 Jul 2013

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.

Jan Simon

### Jan Simon (view profile)

on 20 Jul 2013

Please explain "didn't work" with details. And we have to know, where you have written the shown code.

### Pazzo (view profile)

on 3 Aug 2013

Jan,

I found out that I should add a bracket, [ ],along with an equal sign, =, to make it work.

thank you for your help though.

Pazzo