The CLASS function must be called from a class constructor.

I'm currently working on a project involving some automatic differentiation, and was presented an example code to such an approach. My problems really boil down to me never working with OOD in Matlab before and it seems really overwhelming. The first part of the code looks like this, fairly straight forward. The problem is it won't run past the last line.

function ad = autodiff(val, der)
% A naive autodiff constructor.
ad.val = val;
if nargin == 1
    der = 0.0;
end
if strcmp(der,'variable')
    der = 1.0;
end
ad.der = der;
ad = class(ad, 'autodiff');

I get the error 'The CLASS function must be called from a class constructor', which I do not know how to deal with. How do I create custom classes and then call upon them later?

thanks in advance, Kristian

[James Tursa]

Did you have this file in a directory named '@autodiff', and is the directory that the @autodiff folder is in on the MATLAB path?

[hossein]

would you please explain more about the directory and @autodiff folder

Answer 1

[Cedric]

If you want to learn OOP in MATLAB, have a look at this document: MATLAB Object-Oriented Programming.

Basically, you want to create autodiff.m with a structure that will look like

 classdef autodiff
    properties
       val
       der
    end
    methods
       function self = autodiff(val, der)    % Constructor.
          self.val = val;
          if nargin == 1,  self.der = 0.0;  end
          if strcmp(der,'variable'),  self.der = 1.0;  end
       end
       function self = aMethod(self, ...)
          ...
       end
    end
 end

[Kristian Jørgensen]

Thank you so much. Really helped me out, and I'll be sure to check out your link. Appreciate it.

[Cedric]

You're most welcome!