MATLAB: Use ODE45 with a frequency span instead of time

coupled differential equationsdifferential equationsfrequency spanMATLABode45tspan

I have 2 coupled differential equations. I'm trying to use ODE45, but it requires a time span (tspan).

Is there a way to use a frequency span instead, or perhaps another more suitable differential equation solver?

Best Answer

It does not require that the independent variable be time. It can be whatever your differential equation system requires. If your derivatives are with respect to frequency, use a frequency vector instead.

Related Solutions

MATLAB: ODE solving lack of span inputs

OK, you have 2 coupled ODEs. If I expand the D/Dt(log(V(t))) to 1/V(t)*D/Dt(V(t) I'd get something like this:

function dVdtdcadt = odeperhaps(Vca,t)
k = 12; % perhaps some correction...
V = Vca(1);
ca = Vca(2);
dcadt = k*ca^2;
dVdt = -k*ca*V - dcadt*V/ca;
dVdtdcadt = [dVdt;dcadt];
end

These coupled ODEs you then integrate together. You might want to set the ode-options that ensure the solutions are kept positive - check the help and documentation for ode45 and odeset, it should be the 'NonNegative' field that should be used. That ought to make the V and ca in the denominators safe...

Perhaps I misstyped something.

HTH

MATLAB: Title that spans subplots

An annotation is good to use here. It is a little easier than the text command because the position is relative to the figure -- not one of the axes. Here's an example:

subplot(1,2,1), plot(1:10)
subplot(1,2,2), plot(1:10)
annotation('textbox', [0 0.9 1 0.1], ...
    'String', 'hello, title', ...
    'EdgeColor', 'none', ...
    'HorizontalAlignment', 'center')

If this is just a one-off thing, you can also add an annotation interactively. That is described here in the documentation.

Best Answer

Related Solutions

MATLAB: ODE solving lack of span inputs

MATLAB: Title that spans subplots

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