Construtor does not find external functions

The constructor of a Class does not find a function in an .m file as soon as I move the function .m file to the Class folder, where the Class .m file is. It works as long as the function .m file is in the main folder. What do I have to do so that the constructor finds the fctn in the Class folder?

The error message is: Undefined function 'fctn' for input arguments of type 'double'.

classdef Data

      properties
          propA;
      end

      methods
          function obj = Data (attrA)
                  [obj.propA] = fctn(attrA);
          end
      end
  end

Answer 1

[Matt J]

You could make a private/ folder in the class folder and put your function in there. You could also place the function in the classdef file as a subfunction.

Answer 2

[Steven Lord]

If you want fctn to be a method of class Data that is defined outside the classdef file, you need to define it as a method in the class file itself, then write the implementation in the separate file. See this section of the documentation for more information.

If you want fctn to be a function, not a method, that's accessible to the class but you don't want it to be visible to any other function or class you'll probably want to make it a private function. See the section titled "Access to Functions Defined in Private Folders" in this documentation page. Alternately you could make it a class-related function in the file itself.