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<a name="Function-Overloading"></a>
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<p>
Next: <a href="Operator-Overloading.html#Operator-Overloading" accesskey="n" rel="next">Operator Overloading</a>, Up: <a href="Overloading-Objects.html#Overloading-Objects" accesskey="u" rel="up">Overloading Objects</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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<a name="Function-Overloading-1"></a>
<h4 class="subsection">34.4.1 Function Overloading</h4>
<p>Any Octave function can be overloaded, and allows an 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
</p>
<div 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
</pre><pre class="example">
</pre></div>
<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.
</p>
<div 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><pre class="example">
</pre></div>
<p>which allows polynomials to be plotted in the domain near the region
of the roots of the polynomial.
</p>
<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.
</p>
<div class="example">
<pre class="verbatim">function b = double (a)
b = a.poly;
endfunction
</pre><pre class="example">
</pre></div>
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