k = boundary(x,y) returns
a vector of point indices representing a single conforming 2-D boundary
around the points (x,y). The points (x(k),y(k)) form
the boundary. Unlike the convex hull, the boundary can shrink towards
the interior of the hull to envelop the points.

k = boundary(x,y,z) returns
a triangulation representing a single conforming 3-D boundary around
the points (x,y,z). Each row of k is
a triangle defined in terms of the point indices.

k = boundary(___,s) specifies
shrink factor s using any of the previous syntaxes. s is
a scalar between 0 and 1. Setting s to 0 gives
the convex hull, and setting s to 1 gives
a compact boundary that envelops the points. The default shrink factor
is 0.5.

Boundary point indices, returned as a vector or matrix. k contains
the indices of the input points that lie on the boundary.

For 2-D problems, k is a column
vector of point indices representing the sequence of points around
the boundary, which is a polygon.

For 3-D problems, k is a triangulation
matrix of size mtri-by-3, where mtri is
the number of triangular facets on the boundary. Each row of k defines
a triangle in terms of the point indices, and the triangles collectively
form a bounding polyhedron.

v — Area or volume enclosed by boundary scalar

Area or volume enclosed by boundary, returned as a scalar.

For 2-D problems, v is the area
enclosed by boundary k.

For 3-D problems, v is the volume
enclosed by boundary k.

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