MATLAB® Programming

Object-Oriented Programming Example

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Description | Source Code | Sample Run | Program Notes


The following table will briefly explain how Matlab® creates an object, object constructor, object data and methods as well as compare it to the strategies used in C++.  The examples used in this section match the code in the source section of this page.

Object Component Matlab® Implementation Method C++ Comparison
Declaration Creation of a sub-directory beginning with an "at"(@) symbol accessible through the search path with a name matching that of the object name.
  e.g.  C:\Matlab\@simp_eq
class simp_eq
. . . .
Constructor A file named after the object, containing a function named after the object.
    File:  C:\Matlab\@simp_eq\simp_eq.m
    Contains:  function obj=simp_eq(..param..)
Member Data All data created in the constructor is private and accessable only by member functions.
    obj.domain = [];
Data can be made public or private.  Private data only accessible by member functions.
Member Methods A file with name matching method name, located in object directory.   Accepts the object as a parameter in order to access member data.  If function not located in object directory, then member data is not accessible.
    File:  C:\Matlab\@simp_eq\show.m
    Contains:  function show(se)
          *** se is a simp_eq object
  void show();
Overloaded Operators All MATLAB symbolic operators such as + and - are represented with their appropriate name:  plus and minus.  When a statement uses an expression such as 1+1, MATLAB invokes the plus function for integer values.  Overloading operators is thus very easy.
    File:  C:\Matlab\@simp_eq\plus.m
    Contains:  function out=plus(eq1, eq2)
  simp_eq operator+(simp_eq&);
Using the object once created 1.  Create the object
2.  Call a method
    >> my_eq = simp_eq('sin', linspace(-pi, pi, 100));
    >> show(my_eq);
1.  Create the object
2.  Call a method
    simp_eq my_eq('sin', domain);

Source Code

This first segment of code is the simp_eq.m file located in the @simp_eq directory.   This contains all of the object constructor information.

function s = simp_eq(varargin)
% Name:     simp_eq
% Location: <directory in path>/@simp_eq
% Purpose:  1. Generic object constructor
%           2. Specific constructor
%           3. Copy constructor
% Pre:      No Parameters - Default constructor code used
%           1st Parameter - Simple function type (e.g. 'sin')
%           2nd Parameter - Function domain (default -1 to 1 by 10
%           Object as Parameter - Copy constructor
% Post:     Return a created object
% If no parameters, then default constructor
if nargin == 0
    % Default to sin function
    s.func = ['sin'];
    % Fill the domain with the numbers -1 to 1 by 2/9
    s.domain = linspace(-1, 1, 10);
    % Register this variable as a simp_eq class
    s = class(s, 'simp_eq');
% Else if the parameter is a simp_eq, then copy constructor
elseif isa(varargin{1}, 'simp_eq')
    % Copy the variable
    s = a;
% Otherwise, use a specific constructor
    % If only one parameter passed
    if nargin == 1
        s.func = [varargin{1}];
        s.domain = linspace(-1, 1, 10);
    % If both parameters passed
        s.func = [varargin{1}];
        s.domain = varargin{2};
    % Register this variable as a simp_eq class
    s = class(s, 'simp_eq');

This second segment of code is the show.m file located in the @simp_eq directory.   This contains the object method show which will plot the simple equation.

function show(s)
% Name:     show
% Location: <directory in path>/@simp_eq
% Purpose:  Plot the simple function
% Pre:      N/A
% Post:     Displays screen error if no function is set
%           Displays plot of function otherwise
% Create a new figure window
% Initialize the yvals to zero
yvals = zeros(1,length(s.domain));
% Determine the number of functions for this equation
[neq, w] = size(s.func);
% Evaluate the function over its domain
for i=1:neq
   yvals = yvals + feval(s.func(i,:), s.domain);
% Plot the function
plot(s.domain', yvals');
% Make the shape of the axis square with sides equal
axis('square', 'equal');
% Set the title of the 
title(strcat('Plot of y = ', s.func, ' x'));
% Set the title of the plot
titl = 'Plot of y = ';
for i=1:neq
   if (i == neq)
      titl=strcat(titl, ' ', s.func(i,:), 'x');
      titl=strcat(titl, ' ', s.func(i,:), 'x +');

This third segment of code is the plus.m file located in the @simp_eq directory.   This contains the overloaded object method plus (binary) which will combine two equations to form a new equation with a common domain

function out = plus(eq1, eq2)
% Name:     plus
% Location: <directory in path>/@simp_eq
% Purpose:  Make a new simp_eq by combining the two equations
% Pre:      Two simp_eq's are passed to this function
% Post:     New simp_eq object created with plus
% Construct a new simp_eq from the functions of eq1 and eq2
% As well as the common domain of the two functions
out = simp_eq([eq1.func; eq2.func], ...
   intersect(eq1.domain, eq2.domain));

Sample Run

>> se = simp_eq('sin', linspace(-pi, pi, 100);
>> show(se);
Sample Output Of the simp_eq method show
>> se2 = simp_eq('cos', linspace(-pi, pi, 100);
>> sincosse = se + se2;
simp_eq_plus_out.gif (13046 bytes)

Program Notes

This program requires version 5.1 of Matlab®

This program has been tested, it works perfectly without any errors or warnings.

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Last modified:  12:55 AM on 12/10/1997