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Minimum size vertex separators

Source: R/flow.R
min_st_separators.Rd

List all vertex sets that are minimal \((s,t)\) separators for some \(s\) and \(t\), in an undirected graph.

Usage

min_st_separators(graph)

Arguments

graph

The input graph. It may be directed, but edge directions are ignored.

Value

A list of numeric vectors. Each vector contains a vertex set (defined by vertex ids), each vector is an (s,t) separator of the input graph, for some \(s\) and \(t\).

Details

A \((s,t)\) vertex separator is a set of vertices, such that after their removal from the graph, there is no path between \(s\) and \(t\) in the graph.

A \((s,t)\) vertex separator is minimal if none of its proper subsets is an \((s,t)\) vertex separator for the same \(s\) and \(t\).

Note

Note that the code below returns {1, 3} despite its subset {1} being a separator as well. This is because {1, 3} is minimal with respect to separating vertices 2 and 4.

g <- make_graph(~ 0-1-2-3-4-1)
min_st_separators(g)

#> [[1]]
#> + 1/5 vertex, named:
#> [1] 1
#>
#> [[2]]
#> + 2/5 vertices, named:
#> [1] 2 4
#>
#> [[3]]
#> + 2/5 vertices, named:
#> [1] 1 3

References

Anne Berry, Jean-Paul Bordat and Olivier Cogis: Generating All the Minimal Separators of a Graph, In: Peter Widmayer, Gabriele Neyer and Stephan Eidenbenz (editors): Graph-theoretic concepts in computer science, 1665, 167–172, 1999. Springer.

See also

Other flow: dominator_tree(), edge_connectivity(), is_min_separator(), is_separator(), max_flow(), min_cut(), min_separators(), st_cuts(), st_min_cuts(), vertex_connectivity()

Author

Gabor Csardi csardi.gabor@gmail.com

igraph_all_minimal_st_separators().

Examples


ring <- make_ring(4)
min_st_separators(ring)
#> [[1]]
#> + 2/4 vertices, from 0abce2c:
#> [1] 2 4
#> 
#> [[2]]
#> + 2/4 vertices, from 0abce2c:
#> [1] 1 3
#> 

chvatal <- make_graph("chvatal")
min_st_separators(chvatal)
#> [[1]]
#> + 4/12 vertices, from 664c8f1:
#> [1]  7 10 11 12
#> 
#> [[2]]
#> + 4/12 vertices, from 664c8f1:
#> [1]  3  6  8 11
#> 
#> [[3]]
#> + 4/12 vertices, from 664c8f1:
#> [1]  2  7  9 12
#> 
#> [[4]]
#> + 4/12 vertices, from 664c8f1:
#> [1]  8 10 11 12
#> 
#> [[5]]
#> + 4/12 vertices, from 664c8f1:
#> [1]  6  9 11 12
#> 
#> [[6]]
#> + 4/12 vertices, from 664c8f1:
#> [1]  2  5  7 10
#> 
#> [[7]]
#> + 4/12 vertices, from 664c8f1:
#> [1] 1 3 6 8
#> 
#> [[8]]
#> + 4/12 vertices, from 664c8f1:
#> [1] 2 4 7 9
#> 
#> [[9]]
#> + 4/12 vertices, from 664c8f1:
#> [1]  3  5  8 10
#> 
#> [[10]]
#> + 4/12 vertices, from 664c8f1:
#> [1] 1 4 6 9
#> 
#> [[11]]
#> + 4/12 vertices, from 664c8f1:
#> [1] 1 2 4 5
#> 
#> [[12]]
#> + 4/12 vertices, from 664c8f1:
#> [1] 1 3 4 5
#> 
#> [[13]]
#> + 6/12 vertices, from 664c8f1:
#> [1]  3  6  8 10 11 12
#> 
#> [[14]]
#> + 6/12 vertices, from 664c8f1:
#> [1]  4  6  7  9 11 12
#> 
#> [[15]]
#> + 6/12 vertices, from 664c8f1:
#> [1]  2  4  5  7 10 12
#> 
#> [[16]]
#> + 6/12 vertices, from 664c8f1:
#> [1]  3  4  5  7 10 11
#> 
#> [[17]]
#> + 6/12 vertices, from 664c8f1:
#> [1]  6  7  8  9 11 12
#> 
#> [[18]]
#> + 6/12 vertices, from 664c8f1:
#> [1]  3  5  7  8 10 11
#> 
#> [[19]]
#> + 6/12 vertices, from 664c8f1:
#> [1]  3  4  6  7  9 11
#> 
#> [[20]]
#> + 6/12 vertices, from 664c8f1:
#> [1] 1 3 4 5 6 8
#> 
#> [[21]]
#> + 6/12 vertices, from 664c8f1:
#> [1]  1  2  6  8  9 12
#> 
#> [[22]]
#> + 6/12 vertices, from 664c8f1:
#> [1]  2  5  7  8 10 12
#> 
#> [[23]]
#> + 6/12 vertices, from 664c8f1:
#> [1] 1 2 4 5 7 9
#> 
#> [[24]]
#> + 6/12 vertices, from 664c8f1:
#> [1]  2  7  9 10 11 12
#> 
#> [[25]]
#> + 6/12 vertices, from 664c8f1:
#> [1]  1  6  8  9 11 12
#> 
#> [[26]]
#> + 6/12 vertices, from 664c8f1:
#> [1]  1  2  5  8 10 12
#> 
#> [[27]]
#> + 6/12 vertices, from 664c8f1:
#> [1]  1  3  5  8 10 11
#> 
#> [[28]]
#> + 6/12 vertices, from 664c8f1:
#> [1]  1  2  4  6  9 12
#> 
#> [[29]]
#> + 6/12 vertices, from 664c8f1:
#> [1]  1  3  4  6  9 11
#> 
#> [[30]]
#> + 6/12 vertices, from 664c8f1:
#> [1]  1  2  3  5  8 10
#> 
#> [[31]]
#> + 6/12 vertices, from 664c8f1:
#> [1] 1 2 3 4 6 9
#> 
#> [[32]]
#> + 6/12 vertices, from 664c8f1:
#> [1]  2  3  4  5  7 10
#> 
# https://github.com/r-lib/roxygen2/issues/1092