# Documentation

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# neighbors

Class: TriRep

(Not recommended) Simplex neighbor information

### Note

`neighbors(TriRep)` is not recommended. Use `neighbors(triangulation)` instead.

`TriRep` is not recommended. Use `triangulation` instead.

## Syntax

```SN = neighbors(TR, SI) ```

## Description

`SN = neighbors(TR, SI)` returns the simplex neighbor information for the specified simplices `SI`.

## Input Arguments

 `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`.

## Output Arguments

 `SN` `SN` is an `m`-by-`n` matrix, where `m = length(SI)` , the number of specified simplices, and `n` is the number of neighbors per simplex. Each row `SN(i,:)` represents the neighbors of the simplex `SI(i)`.By convention, the simplex opposite `vertex(j)` of simplex `SI(i)` is `SN(i,j)`. If a simplex has one or more boundary facets, the nonexistent neighbors are represented by `NaN`.

## Examples

### Example 1

Load a 3-D triangulation and use `TriRep` to compute the neighbors of all tetrahedra.

```load tetmesh trep = TriRep(tet, X) nbrs = neighbors(trep) ```

### Example 2

Query a 2-D triangulation created using `DelaunayTri`.

```x = rand(10,1) y = rand(10,1) dt = DelaunayTri(x,y)```
Find the neighbors of the first triangle:
`n1 = neighbors(dt, 1)`

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