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<h3 class="section">29.3 Convex Hull</h3>
<p>The convex hull of a set of points is the minimum convex envelope
containing all of the points. Octave has the functions <code>convhull</code>
and <code>convhulln</code> to calculate the convex hull of 2-dimensional and
N-dimensional sets of points.
<!-- ./geometry/convhull.m -->
<p><a name="doc_002dconvhull"></a>
<div class="defun">
— Function File: <var>H</var> = <b>convhull</b> (<var>x, y</var>)<var><a name="index-convhull-2113"></a></var><br>
— Function File: <var>H</var> = <b>convhull</b> (<var>x, y, opt</var>)<var><a name="index-convhull-2114"></a></var><br>
<blockquote><p>Returns the index vector to the points of the enclosing convex hull. The
data points are defined by the x and y vectors.
<p>A third optional argument, which must be a string, contains extra options
passed to the underlying qhull command. See the documentation for the
Qhull library for details.
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<p class="noindent"><strong>See also:</strong> <a href="doc_002ddelaunay.html#doc_002ddelaunay">delaunay</a>, <a href="doc_002dconvhulln.html#doc_002dconvhulln">convhulln</a>.
</p></blockquote></div>
<!-- ./DLD-FUNCTIONS/convhulln.cc -->
<p><a name="doc_002dconvhulln"></a>
<div class="defun">
— Loadable Function: <var>h</var> = <b>convhulln</b> (<var>p</var>)<var><a name="index-convhulln-2115"></a></var><br>
— Loadable Function: <var>h</var> = <b>convhulln</b> (<var>p, opt</var>)<var><a name="index-convhulln-2116"></a></var><br>
— Loadable Function: [<var>h</var>, <var>v</var>] = <b>convhulln</b> (<var><small class="dots">...</small></var>)<var><a name="index-convhulln-2117"></a></var><br>
<blockquote><p>Return an index vector to the points of the enclosing convex hull.
The input matrix of size [n, dim] contains n points of dimension dim.
<p>If a second optional argument is given, it must be a string or cell array
of strings containing options for the underlying qhull command. (See
the Qhull documentation for the available options.) The default options
are "s Qci Tcv".
If the second output <var>V</var> is requested the volume of the convex hull is
calculated.
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<p class="noindent"><strong>See also:</strong> <a href="doc_002dconvhull.html#doc_002dconvhull">convhull</a>, <a href="doc_002ddelaunayn.html#doc_002ddelaunayn">delaunayn</a>.
</p></blockquote></div>
<p>An example of the use of <code>convhull</code> is
<pre class="example"> x = -3:0.05:3;
y = abs (sin (x));
k = convhull (x, y);
plot (x(k), y(k), "r-", x, y, "b+");
axis ([-3.05, 3.05, -0.05, 1.05]);
</pre>
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