ode45 - return a column vector

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Ojaswita 2013-5-14

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https://ww2.mathworks.cn/matlabcentral/answers/75725-ode45-return-a-column-vector

编辑： Ali Amirfaridi 2021-4-30

采纳的回答： Jan

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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!

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Walter Roberson 2018-1-7

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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 2019-11-30

Hoda Khesali Aghtaei comments to me:

was helpful

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采纳的回答

Jan 2013-5-14

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https://ww2.mathworks.cn/matlabcentral/answers/75725-ode45-return-a-column-vector#answer_85392

编辑：Jan 2013-5-14

在 MATLAB Online 中打开

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.