Calculates the neighborhood-inclusion preorder of an undirected graph.

## Details

Neighborhood-inclusion is defined as $$N(u)\subseteq N[v]$$ where \(N(u)\) is the neighborhood of \(u\) and \(N[v]=N(v)\cup \lbrace v\rbrace\) is the closed neighborhood of \(v\). \(N(u) \subseteq N[v]\) implies that \(c(u) \leq c(v)\), where \(c\) is a centrality index based on a specific path algebra. Indices falling into this category are closeness (and variants), betweenness (and variants) as well as many walk-based indices (eigenvector and subgraph centrality, total communicability,...).

## References

Schoch, D. and Brandes, U., 2016. Re-conceptualizing centrality in social networks.
*European Journal of Applied Mathematics* 27(6), 971-985.

Brandes, U. Heine, M., Müller, J. and Ortmann, M., 2017.
Positional Dominance: Concepts and Algorithms.
*Conference on Algorithms and Discrete Applied Mathematics*, 60-71.

## Examples

```
library(igraph)
# the neighborhood inclusion preorder of a star graph is complete
g <- graph.star(5, "undirected")
P <- neighborhood_inclusion(g)
comparable_pairs(P)
#> [1] 1
# the same holds for threshold graphs
tg <- threshold_graph(50, 0.1)
P <- neighborhood_inclusion(tg)
comparable_pairs(P)
#> [1] 1
# standard centrality indices preserve neighborhood-inclusion
data("dbces11")
P <- neighborhood_inclusion(dbces11)
is_preserved(P, degree(dbces11))
#> [1] TRUE
is_preserved(P, closeness(dbces11))
#> [1] TRUE
is_preserved(P, betweenness(dbces11))
#> [1] TRUE
```