MATLAB: Very basic object oriented question

methodsobject oriented programmingoop

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

Best Answer

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

Related Solutions

MATLAB: Property validation in subclass

Note: I would recommeng giving a name other than set to your property. That name is already overloaded enough by matlab.

You can create a property validation function in the class that define the property using the syntax (for handle classes):

function set.propertyname(object, valuetoset)
    %validation code
end

with your property name this would be

function set.set(this, value)     %See why you should rename the property?
   if ~strcmp(class(value), somevalidclass)
        error('invalid class supplied to set');
   end
   this.set = value;
end

However, as I said, this property set method must be implemented in the class that defines the property, that is your base class, not the derived class. The workaround is from the set method to call another method that does the validation and is overridden by the derived class:

classdef SimpleList < handle
    properties
        set;
    end
      methods
          function set.set(this, value)
              isok = this.validateset(value);  
              if ~isok
                 error('invalid type of variable for set property)
              end
              this.set = value;  %DO NOT set the value is a subfunction or you'll get infinite recursion
          end
      end
      methods (Access = protected)
          function isok = validateset(this, value)
             isok = true;
          end
      end
  end
classdef ObjList < SimpleList
    methods (Access = protected)
        function isok = validateset(this, value)
           isok = strcmp(class(value), 'double');
        end
    end
end

MATLAB: What is wrong of this class

What is the error you are receiving? I saved your test code to file (dummy.m) and it seemed to work.

Best Answer

Related Solutions

MATLAB: Property validation in subclass

MATLAB: What is wrong of this class

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