MATLAB and Simulink resources for Arduino, LEGO, and Raspberry Pi

Learn moreOpportunities for recent engineering grads.

Apply Today**New to MATLAB?**

Asked by Kristian Jørgensen
on 5 Feb 2013

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

*No products are associated with this question.*

Answer by Cedric Wannaz
on 5 Feb 2013

Edited by Cedric Wannaz
on 5 Feb 2013

Accepted answer

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
on 5 Feb 2013

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

## 1 Comment

## James Tursa (view profile)

Direct link to this comment:http://www.mathworks.com/matlabcentral/answers/62307#comment_127408

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