# isConnected

Class: triangulation

Test if two vertices are connected by edge

## Syntax

`tf = isConnected(TR,vstart,vend)tf = isConnected(TR,E)`

## Description

`tf = isConnected(TR,vstart,vend)` returns a `logical` array of `true` or `false` values that indicate whether the specified pairs of vertices are connected by an edge. Element `tf(j)` is `true` when the vertices, `vstart(j)` and `vend(j)`, are connected by an edge.

`tf = isConnected(TR,E)` specifies the edge start and end indices in matrix `E`. Element `tf(j)` is `true` when the vertices, `E(j,1)` and `E(j,2)`, are connected by an edge.

## Input Arguments

 `TR` Triangulation representation, see `triangulation` or `delaunayTriangulation`. `vstart` IDs of start vertices, specified as a column vector. Each vertex ID refers to a vertex at the start of an edge. `vend` IDs of end vertices, specified as a column vector. Each vertex ID refers to a vertex at the end of an edge. `E` IDs of the edge vertices, specified as a two-column matrix. Each row of `E` corresponds to a candidate edge and contains two IDs:`E(j,1)` is the ID of the vertex at the start of a candidate edge. `E(j,2)` is the ID of the vertex at end of the edge.

## Output Arguments

 `tf` Logical values, returned as a column vector. Element `tf(j)` is `true` when either of the following are true:The vertices, `vstart(j)` and `vend(j)`, are connected by an edge.The vertices, `E(j,1)` and `E(j,2)`, are connected by an edge.Otherwise, `tf(j)` is false.

## Definitions

### Vertex ID

A row number of the matrix, `TR.Points`. Use this ID to refer a specific vertex in the triangulation.

## Examples

expand all

### Determine Whether Vertices are connected by an Edge in 2-D

```load trimesh2d TR = triangulation(tri,x,y);```

Determine whether vertices `3` and `117` are connected by an edge.

`isConnected(TR,3,117)`
```ans = 1```

The vertices are connected by an edge.

Determine whether vertices `3` and `164` are connected by an edge.

`isConnected(TR,3,164)`
```ans = 0```

The vertices are not connected by an edge.

### Determine Whether Vertices are connected by an Edge in 3-D

```X = gallery('uniformdata',[10,3],0); DT = delaunayTriangulation(X);```

Determine whether vertices `2` and `7` are connected by an edge.

```E = [2 7]; isConnected(DT,E)```
```ans = 1```

The vertices are connected by an edge.