Saving each vector of an ode45 vector solution in a matrix.

I have the following code, where I am using a different value of a parameter G in my ODE system (solving it w/ ode45) and want to plot each solution on the same graph. It isnt the same as IC's, as these are the same but the parameter varies. Currently I have:

for i=1:20

G=i/20 %Saving that iterates value of G

[phi,y]=ode45(@(phi,y) odefun(phi,y,G), timerange, IC);

z(i,;)=y %

end

then I want to save all these y's without creating 20 vectors. Is there a way to save each vector y as a column of a matrix? I am very lost and any direction would be very helpful, I cannot find a thread or anythign on the helpcenter.

Thanks in advance

[James Tursa]

y will be output as a column vector for scalar problems, or a matrix for more than 1D problems. Which situation do you have? I.e., what is size(y)?

[J. Alex Lee]

Another important question is if "timerange" are just the 2 point limits of time, or a vector; if just the limits, each version may produce different length of y (even if it was 1D problem). In such a case, you couldn't [easily] use a matrix to store the results anyway.

[Gabriel Venter]

I have a 2D autuonomous ODE system here. And I was worried about this timestep problem since ode45 uses a variable timestep and that would be different for different G, so clearly what I was doing was stupid. Thanks!

Answer 1

[J. Alex Lee]

Use a cell array instead

z = cell(1,20)
for i=1:20
    G=i/20 %Saving that iterates value of G
    [phi,y]=ode45(@(phi,y) odefun(phi,y,G), timerange, IC);
    z{i}=y %
end

Or better yet just use the solution structure version of output

for i=20:-1:1
    G=i/20 %Saving that iterates value of G
    sol(i) = ode45(@(phi,y) odefun(phi,y,G), timerange, IC);
end

[Gabriel Venter]

Thank you! Lifesaver. What does the extra "20:-1:1" bit mean there, and why is it in that last loop but not the first?

[J. Alex Lee]

glad it helped!

"20:-1:1" is going backwards, so the pre-allocation of the structure array is implied. Didn't need to do it with the cell array version since it was straightforward to pre-allocate an empty cell array. You could loop backward on that example as well, and wouldn't need to do the explicit pre-allocation.