Simple question about creating an anonymous function,

Hi @Noob,

In MATLAB, when you create an anonymous function like myrhs = @(t, z) model(t, z, p), you are indeed specifying the inputs to the model, which are the current time t and the current state z. The parameter structure p is not included in the anonymous function because it is treated as a constant or fixed parameter that does not change during the integration process. The ode45 solver calls myrhs multiple times during its execution, passing different values of t and z while keeping p constant. This is a common practice in MATLAB to simplify the function signature when the parameters do not vary. If you were to include p in the anonymous function, it would imply that p could change with each call, which is not the case here. Thus, the correct interpretation is that @(t, z) specifies the inputs to the model, allowing ode45 to efficiently compute the solution while treating p as a fixed parameter. Here is a simple example for clarity:

function dzdt = model(t, z, p)
  dzdt = p.mass * z; % Example equation
end

p.mass = 5; % Example parameter
myrhs = @(t, z) model(t, z, p); % Anonymous function without p
[t, z] = ode45(myrhs, [0 10], initial_conditions);

In this example, p is fixed, and myrhs only needs t and z as inputs.

Hope this helps.