Triangle or tetrahedron neighbors



N = neighbors(TR) returns the IDs of the neighbors to all triangles or tetrahedra in TR. N is a 3-column (2-D) or 4-column (3-D) matrix whose rows contain the IDs of the neighboring triangles or tetrahedra to that element in the triangulation.


N = neighbors(TR,ID) returns the neighbors of the triangles or tetrahedra specified in ID.

By convention, the (i,j) element of N is the neighbor opposite to the jth vertex of the ith element of ID.


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Find neighboring tetrahedra in a 3-D triangulation.

Create a 3-D triangulation.

load tetmesh
TR = triangulation(tet,X);

Compute the IDs of the neighboring tetrahedra to each element of the triangulation.

N = neighbors(TR);

Display the IDs of the neighbors to the fifth tetrahedron.

ans = 1×4

        2360        1539           2        1851

Examine the vertex IDs of the first neighbor.

ans = 1×4

        1093         891         893         858

Find neighboring triangles in a 2-D Delaunay triangulation.

Create a 2-D Delaunay triangulation.

x = rand([10,1]);
y = rand([10,1]);
TR = delaunayTriangulation(x,y);

Find the neighbors of the first triangle. NaN indicates that the triangle is on the boundary of the triangulation and only has two neighbors.

N = neighbors(TR,1)
N = 1×3

   NaN     4     3

Examine the vertex IDs of the third neighbor.

ans = 1×3

     5     2     8

Input Arguments

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Triangulation representation, specified as a scalar triangulation or delaunayTriangulation object.

Data Types: triangulation | delaunayTriangulation

Triangle or tetrahedron IDs, specified as a scalar or a column vector whose elements correspond to a single triangle or tetrahedron in the triangulation object. The ID of each triangle or tetrahedron is the corresponding row number of the ConnectivityList property.

If a triangle or tetrahedron has one or more boundary facets, the nonexistent neighbors are represented as NaN values in N.

Data Types: double

Introduced in R2013a