Note:

SN = neighbors(TR, SI)
SN = neighbors(TR, SI)
returns the simplex
neighbor information for the specified simplices SI
.
TR  Triangulation representation. 
SI  SI is a column vector of simplex indices
that index into the triangulation matrix TR.Triangulation .
If SI is not specified the neighbor information
for the entire triangulation is returned, where the neighbors associated
with simplex i are defined by the i 'th
row of SN . 
SN 
By convention,
the simplex opposite 
A simplex is a triangle/tetrahedron or higherdimensional equivalent. A facet is an edge of a triangle or a face of a tetrahedron.
Load a 3D triangulation and use TriRep
to
compute the neighbors of all tetrahedra.
load tetmesh trep = TriRep(tet, X) nbrs = neighbors(trep)
Query a 2D triangulation created using DelaunayTri
.
x = rand(10,1) y = rand(10,1) dt = DelaunayTri(x,y)
n1 = neighbors(dt, 1)