Very basic object oriented question

Hello,

I'm trying to call a method of a class in order to calculate one of the properties of the class, but I'm getting an error.

 classdef Module
    properties
        Parameters;
        StateVariables;
        ControllableInputs;
        StateSpace;
    end

    methods
        function this =Module(Parameters,StateVariables,ControllableInputs)
            % class constructor
            if(nargin > 0)
                this.Parameters = Parameters;
                this.StateVariables  = StateVariables;
                this.ControllableInputs = ControllableInputs;
                this.StateSpace = FindStateSpace(Parameters,StateVariables,ControllableInputs);
            end
        end
       function StateSpace =   FindStateSpace(Parameters,StateVariables,ControllableInputs)
             ....
        end
    end
 end

This is producing an error "Undefined function 'FindStateSpace' for input arguments of type 'sym'." Can someone please tell me what I'm doing incorrectly, and how to fix this problem? I think this is probably a very very basic question, but I'm a novice with MATLAB object oriented programming.

Thank you, Kevin

Answer 1

[Eric]

I don't believe you're allowed to call non-static class methods from within the constructor itself. Until the constructor returns, the variable "this" is not known to be of class Module.

Since you're passing in Parameters, StateVariables, and ControllableInputs as inputs to the FindStateSpace method, I think an easy work around is to make it a static method.

Before the final "end" statement of this file, do something like:

methods(Static)
  function StateSpace = FindStateSpace(Parameters, StateVariables, ControllableInputs)
    ....

    end

end

In the constructor, use the static method as follows:

this.StateSpace = Module.FindStateSpace(Parameters,StateVariables,ControllableInputs);

Good luck,

Eric

[Kevin Bachovchin]

Thanks, I had a feeling there was a really easy solution.

Answer 2

[per isakson]

Try this:

    >> mm = my_class
    mm = 
      my_class with properties:

        prop: 17

where

    classdef  my_class
        properties  
            prop
        end

        methods
            function this = my_class(  )
                this.prop = this.my_method();
            end
            function val = my_method( this )
               val = 17; 
            end
        end
    end

.

AFAIK: You can /should not have a property and a method with the same name, StateSpace

.

And static

    mm = 
      my_class with properties:

        prop: 17
where

    classdef  my_class
        properties  
            prop
        end

        methods
            function this = my_class(  )
                this.prop = my_class.my_method();
            end
        end
        methods( Static = true )
            function val = my_method()
               val = 17; 
            end
        end
    end