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29.3 Convex Hull

The convex hull of a set of points, is the minimum convex envelope containing all of the points. Octave has the functions convhull and convhulln to calculate the convec hull of 2-dimensional and N-dimensional sets of points.

— Function File: H = convhull (x, y)
— Function File: H = convhull (x, y, opt)

Returns the index vector to the points of the enclosing convex hull. The data points are defined by the x and y vectors.

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.

     
     
See also: delaunay, convhulln.

— Loadable Function: H = convhulln (p)
— Loadable Function: H = convhulln (p, opt)

Returns an index vector to the points of the enclosing convex hull. The input matrix of size [n, dim] contains n points of dimension dim.

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".

     
     
See also: convhull, delaunayn.

An example of the use of convhull is

     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]);