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Next:&nbsp;<a rel="next" accesskey="n" href="Operator-Overloading.html#Operator-Overloading">Operator Overloading</a>,
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<h4 class="subsection">33.4.1 Function Overloading</h4>

<p>Any Octave function can be overloaded, and allows a object specific
version of this function to be called as needed.  A pertinent example
for our polynomial class might be to overload the <code>polyval</code> function
like

<pre class="example"><pre class="verbatim">     function [y, dy] = polyval (p, varargin)
       if (nargout == 2)
         [y, dy] = polyval (fliplr(p.poly), varargin{:});
       else
         y = polyval (fliplr(p.poly), varargin{:});
       endif
     endfunction
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   <p>This function just hands off the work to the normal Octave <code>polyval</code>
function.  Another interesting example for an overloaded function for our
polynomial class is the <code>plot</code> function.

<pre class="example"><pre class="verbatim">     function h = plot(p, varargin)
       n = 128;
       rmax = max (abs (roots (p.poly)));
       x = [0 : (n - 1)] / (n - 1) * 2.2 * rmax - 1.1 * rmax;
       if (nargout > 0)
         h = plot(x, p(x), varargin{:});
       else
         plot(x, p(x), varargin{:});
       endif
     endfunction</pre>
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   <p class="noindent">which allows polynomials to be plotted in the domain near the region
of the roots of the polynomial.

   <p>Functions that are of particular interest to be overloaded are the class
conversion functions such as <code>double</code>.  Overloading these functions
allows the <code>cast</code> function to work with the user class and can aid
in the use of methods of other classes with the user class.  An example
<code>double</code> function for our polynomial class might look like.

<pre class="example"><pre class="verbatim">     function b = double (a)
       b = a.poly;
     endfunction
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