Troubleshooting ODE45 Matlab Subfunction: Save Matrix Values in Main Code

[hasek]

I'm stuck with a problem with the subfunction ODE45 of Matlab:

I need to save two matrixes' values created inside the ODE subfunction.
I can't create an index inside the subfunction because I have to define it at the start so at every round it returns to zero.

This is what I've done in the main:

t0 = 0;
tf = 450;
y0 = [0 0 0 0 0 0];
options = odeset('RelTol', 1e-6);
[t, y] = ode45('ac_im3_IPM_prova1', [t0,tf] , y0, options);

and this is the subfunction:

function yp = ac_im3_IPM_prova1(t, y);
.
.
.
vsd = 2/3 * (vsa * cos(ttg) + vsb * cos(ttg - 2*pi/3) + vsc * cos(ttg - 4*pi/3));
vsq = -2/3 * (vsa * sin(ttg) + vsb * sin(ttg - 2*pi/3) + vsc * sin(ttg - 4*pi/3));
.
.
.
yp(1) = (vsd - Rs*isd + (wge)*fsq);
yp(2) = (vsq - Rs*isq - (wge)*fsd);
yp(3) = ( - Rr*ird + (wge-p*wm)*frq);
yp(4) = ( - Rr*irq - (wge-p*wm)*frd);
yp(5) = (tm - (TL + KD*wm)) / J;
yp(6) = wge;

yp = yp';

I'd like to save vsd and vsq values of every round in a matrix or in someway!

 

[J77]

You could always write you own one-line (fixed step-size) RK4 code.

 

[hasek]

Ok, now I created an index inside the subfunction in this way:

i=0;
if t ~= 0
load('i');
end
i=i+1;
save('i');

Now there is another problem:

I'm wondering if this procedure could affects the simulation time returning me wrong values

 

[FlvD]

Hey i need help in ODE45 too

i have the following code

>>for i=1:5
>>tspan=[0 30]
>>h0=Hv(i)
>>[t,h]=ode45['a ODEfunction',tspan,h0]
>>plot(t,h)
>>end

in this loop how can i save 5 values of [t,h],
as t, h produces each loop run like follows
t=
1
2
3
4
.
.
.
h=
5
6
7
8..

also i need to plot all of them n i could view the 5 graphs them..pls help..

 

[alphy]

I would recommend using the "OutputFcn" option in the ode45 function to save the values of vsd and vsq at each time step. This option allows you to specify a function that will be called at each time step and can be used to save any desired variables.

For example, you could create a new function, let's call it "save_values", that takes in the current time and state variables (vsd and vsq) and stores them in a matrix. Then, in your main code, you can use the "OutputFcn" option to call this function at each time step and save the values.

Another option could be to use global variables to store the values of vsd and vsq within the subfunction and then access them in the main code after the ode45 function has finished running. However, this approach is not recommended as it can lead to potential errors and is not considered good programming practice.

I hope this helps you in troubleshooting your issue with saving the matrix values in your main code. It's important to carefully consider your options and choose the most appropriate solution for your specific problem.