boundary {graph} | R Documentation

## Returns the Boundary between a Graph and a SubGraph

### Description

The boundary of a subgraph is the set of nodes in the original graph that have edges to nodes in the subgraph. The function `boundary` computes the boundary and returns it as a list whose length is the same length as the number of nodes in the subgraph.

### Usage

    boundary(subgraph, graph)

### Arguments

`graph` | the original graph from which the boundary will be created
`subgraph` | can either be the vector of the node labels or the subgraph itself.

### Details

The boundary of a subgraph is the set of nodes in the graph which have an edge that connects them to the specified subgraph but which are themselves not elements of the subgraph.

For convenience users can specify the subgraph as either a graph or a vector of node labels.

### Value

This function returns a named list of length equal to the number of nodes in `subgraph`. The elements of the list correspond to the nodes in the `subgraph`. The elements are lists of the nodes in `graph` which share an edge with the respective node in `subgraph`.

### Author(s)

Elizabeth Whalen and R. Gentleman

### See Also

`subGraph`, `graph-class`

### Examples

      set.seed(123)
      g1 <- randomGraph(letters[1:10], 1:4, p=.3)
      ##both should be "a"
      boundary(c("g", "i"), g1)

[Package graph version 1.72.0 Index]