creating rational class constructor in matlab - matlab

Question

suppose we have following class,i want to declare rational number class in matlab,i am beginner of object oriented programming in matlab languages and i want to learn basics
classdef ratnum %rational number class
properties (Access=protected)
n %numerator
d %denomerator
end
methods
function r=ratnum(numerator,denomenator)
r.n=numerator;
r.d=denomenator;
end
end
end
how can i create constructor with specific values in matlab main part?should i use name of class ?thanks in advance

Answer 1

To instantiate an object of this class you can use: num1 = ratnum(2,3)
Since MATLAB doesn't have method overloading that is based on the amount of passed inputs, you could use nargin to select the correct scenario, as follows:
classdef ratnum %rational number class
properties (Access=protected)
n %//numerator
d %//denominator
end
methods
function r = ratnum(numerator,denominator)
switch nargin
case 2
r.n=numerator;
r.d=denominator;
case 0
%//whatever you want the defaults to be
end
end
end
end
A simple debug trick is to do num1_str=struct(num1) which allows you to see the contents of the object. However, you should create some public methods to get the values (instead of turning the object to a struct every time).
To overload the default summation of MATLAB you need to understand that whenever you write a+b it is automatically translated into plus(a,b). When defining custom classes with custom summation you should make a folder that has the name #classname (in your case #ratnum) and in it:
ratnum.m: the class definition file (which is the code you wrote)
a file named plus.m which looks something like:
.
function sum = plus(ratnum1,ratnum2)
ratnum1 = ratnum(ratnum1);
ratnum2 = ratnum(ratnum2);
sum = (...
ratnum1.r*ratnum2.d + ...
ratnum2.r*ratnum1.d )/ ...
(ratnum1.d * ratnum2.d);
end
Then, when you use + to add ratnums it will use the correct plus function.
Here's some helpful reading: MATLAB Documntation: Implementing Operators for Your Class
To call class methods, even from within other class methods, you must always write the class name first: ratnum.sum(ratnum1). Here's an example:
classdef ratnum %rational number class
properties (Access=public)
n %//numerator
d %//denominator
end
methods (Access = public)
function r = ratnum(numerator,denominator)
switch nargin
case 2
r.n=numerator;
r.d=denominator;
case 0
%whatever you want the defaults to be
end
end
end
methods (Access = public, Static)
function out = sum(ratnum)
out = ratnum.n + ratnum.d;
end
end
end
then:
>> a = ratnum(1,1)
a =
ratnum with properties:
n: 1
d: 1
>> ratnum.sum(a)
ans =
2

Answer 2

If you want to overload constructor with many different forms you'll have to initialize missing parameters with default value (or use varargin for more complex overloads):
function [r] = ratnum(num, den, varargin)
% Showing initializing missing parameters
if (nargin < 2), den = 42; end
if (nargin < 1), num = 7; end
% Showing working with varargin
if (nargin == 3)
...
elseif((nargin > 1) && (ischar(varargin{1}))
...
else
...
end
end
If you want to create named initializers for clarification of their meaning, you'll have to do it with Static methods:
methods (Static)
function [r] = TwoThird()
r = ratnum(2, 3);
end
function [r] = Half()
r = ratnum(1, 2);
end
end
Which can be used like this:
dummy = ratnum.Half(); % Ratio is 1/2
dummy = ratnum.TwoThird(); % Ratio is 2/3
dummy = ratnum(42, 666); % Ratio can be any custom one