ode45 - return a column vector

Below is the function i have described:

function ssir = fnsir(t,y)
b = 0.1; 
q = 0.022; 
m = 0.012; 
l = 0.125;  
r = 0.14;  
ssir(1) = q - m*y(1)-b*y(1)*y(2)+ l*y(3);
ssir(2) = (b*y(1)*y(2))-((m+r)*y(2));
ssir(3) = (r*y(2)) - (y(3)*(m+r));
------------------------------

And i am calling this function using:

[t,y]=ode45('fnsir', [0 10], [200 20 2])

and i am getting the following error:

??? Error using ==> odearguments at 113 FNSIR must return a column vector.

Error in ==> ode45 at 173 [neq, tspan, ntspan, next, t0, tfinal, tdir, y0, f0, odeArgs, odeFcn, ...

--------------------------

can anyone please help me sort this out

Thanks!

[SAFA BOUDHRAA]

I'am having the same problem, but the solution mentioned doesn't help

[Walter Roberson]

SAFA BOUDHRAA: As the very last step of your function, turn the output into a column vector. For example if you currently have

function dy = MyOde(....)
  ...
  dy = ....

then after that do

   dy = dy(:);

as the last thing before returning. The variable you should do this to is the one returned by your function.

If that does not work, then use the debugger to check whether possibly you are returning the empty vector.

[Walter Roberson]

Hoda Khesali Aghtaei comments to me:

was helpful

Answer 1

[Jan]

ODE45 expects the reply as [3 x 1] vector, but your code creates a [1 x 3] vector. Two solutions:

1. Pre-allocate ssir as a vector of the wanted shape:

ssir = zeros(3, 1);
ssir(1) = ...

2. Or append a reshaping as last line of the function fnsir:

ssir = ssir(:);

As you see, the error message is rather clear. It is worth to read Matlab's messages carefully. They are the best messages I've ever seen in a commercial software.

[Ojaswita]

Thanks alot for the help!

Actually, people like me are new to certain parts of MATLAB and sometimes I do not know hoe to solve the problem, hence the requests for help!

Thanks alot once again, your help is much appreciated!!

[Jan]

Your questions are welcome in the forum. And I know, that one can desperate on such tiny details. Therefore I spend time in this forum to answer and I'm very happy about the time, TMW has spent to create the helpful error messages - compared to the confusing stuff show by e.g. Microsoft programs...

[Ojaswita]

Yaa... smal small things like this sometimes take days and days... thanks to all the helpful peers around here!!!

[Frank Böhnke]

thanks very much, that answer helped on the 19 th Dec 2016 Frank, Munich

[SY]

Wow, I've been trying to fix this exact problem for my program and this answer from four years ago really helped me. Thanks!

[Kalpit Bakal]

Thank you so much for the answer. My code work perfectly after this. Best part about peer to peer learning!

[Ali Amirfaridi]

still helping in 2020! thank you mate

[Yashee Sinha]

thanks a lot!