Using Object Properties with ODE45

Hi All

I'm using ODE45 with my ODEs contained in the function derivs, i.e.,

[T,Y] = ode45(@(t,y)derivs(t,y,obj),[0 10],[0 0]);

The variable obj is an object which I use to perform some logical tests within derivs, i.e.,

function dy = derivs(t,y,obj)

if (t>obj.parameter1)
   % Update parameter 1
   obj.parameter1 = ... %some new value
end

dy = zeros(2,1);
dy(1) = ...
dy(2) = ...  

end

The logical 'if' test works for the value of obj.parameter1 that is set when I initially call the constructor for the class obj, and appears to update obj.parameter1 with a new value when I view the object at the command line. However, for all subsequent calls to derivs the logical 'if' appears to be comparing t with the initial value of obj.parameter1 (i.e. the value initialised to it at construction) rather than the updated value in the if statement.

I can't figure this out since as far as I can tell obj.parameter1 is being updated in the object, but not in the if statement (all parameters are public in the class definition). I have a similar implementation in C++, and it works fine there.

Any ideas??

Many thanks

James

Answer 1

[James Briaris]

Okay, so it's to do with the way Matlab holds the object in memory. Changes to properties doesn't appear to change the original value defined in the constrcutor. Instead it makes the change to a copy of the parameter. Appending '< handle' to the class definition allows you to change the original parameter values on the fly, i.e.,

classdef MyClass < handle 

properties

methods

end

Whilst this fixes my problem, I'm a little loss for the reason for this extra layer of complexity. Perhaps I'm to used to C++, but the OOP functionality in C++ certainly seems more intuitive.