Error in a ODE in a loop (returns a vector of length 9, but the length of initial conditions vector is 2)

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Paul Rogers 2021-2-1

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评论： Walter Roberson 2021-2-3

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Hi everybody, and thanks again for the help.

I run the file ciclo_1_bis, which loads from the file z_matlab_1 different vectors, and at every loop

it updates the initial condition, and other parameters stored in z_general_1.

First loop (j=1) ok, the when j=2 it says this erroor message:

Error using odearguments (line 92)
GREITZER returns a vector of length 9, but the length of initial conditions vector is 2. The vector returned by
GREITZER and the initial conditions vector must have the same number of elements.
Error in ode113 (line 113)
[neq, tspan, ntspan, next, t0, tfinal, tdir, y0, f0, odeArgs, odeFcn, ...
    

what could be possibily wrong? It just changes the initial conditions and the time for the next loop.

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Walter Roberson 2021-2-2

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When you

save main_parameters.mat

after the first loop, then the workspace includes the t that was the result of the [t,y] = ode113() call.

When you load() that .mat inside the function, that t gets pulled inside the workspace, replacing the t that was passed in as a function parameter.

Don't DO that. Do not save() and load() like that. Pass the values in to the function, either individually or as part of a structure. http://www.mathworks.com/help/matlab/math/parameterizing-functions.html

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Walter Roberson 2021-2-2

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Yes. However it is more secure to explicitly save only the variables you need, and it is more robust to only load the variables you need. It is also more robust to call load() as a function, giving you a struct result with one field per variable, and pulling values out of the struct as needed.

Using save() the way you are is slower and more prone to error.

The changes are not difficult. I will send you the revised version after you answer this:

You have

gamma_T = @(v) A*sin(w*t)+b; % valve's function

which you invoke at gamma_t(t) . What is the point of that function? You do not use v in the body of the function, so the creation of the anonymous function would look up the current values of A, w, t, and b, and "lock them in" to the function handle, causing gamma_T to return the same value each time it was invoked. You then confuse the reader by calling gamma_T(t) which might lead them to think that the (t) value being passed in to gamma_T had some effect on the calculation, that it would become the t mentioned in the body of the anonymous function.. but it will not be. The parameter you pass in to the anonymous function will be ignored.

And since you only call it once, with one value of t, why bother making it a function anyhow? Why not just make it a plain variable?