neighbors

Triangle or tetrahedron neighbors

Syntax

N = neighbors(TR)

N = neighbors(TR,ID)

Description

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.

Examples

3-D Triangulation

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.

N(5,:)

ans = 1×4

        2360        1539           2        1851

Examine the vertex IDs of the first neighbor.

TR.ConnectivityList(N(1),:)

ans = 1×4

        1093         891         893         858

2-D Delaunay Triangulation

Find neighboring triangles in a 2-D Delaunay triangulation.

Create a 2-D Delaunay triangulation.

rng('default')
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

     4     8     5

Examine the vertex IDs of the third neighbor.

TR.ConnectivityList(N(3),:)

ans = 1×3

     3     8     2

Input Arguments

TR — Triangulation representation

scalar triangulation object

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

Data Types: triangulation | delaunayTriangulation

ID — Triangle or tetrahedron IDs

scalar | column vector

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

Extended Capabilities

Thread-Based Environment

Run code in the background using MATLAB® backgroundPool or accelerate code with Parallel Computing Toolbox™ ThreadPool.

This function fully supports thread-based environments. For more information, see Run MATLAB Functions in Thread-Based Environment.

Version History

Introduced in R2013a