Calculates the transitive reduction of a partial ranking.

`transitive_reduction(P)`

- P
A partial ranking as matrix object calculated with neighborhood_inclusion or positional_dominance.

transitive reduction of `P`

```
library(igraph)
g <- threshold_graph(100, 0.1)
P <- neighborhood_inclusion(g)
sum(P)
#> [1] 5647
R <- transitive_reduction(P)
sum(R)
#> [1] 181
```