Calculate the maximal and minimal rank possible for each node
in any ranking that is in accordance with the partial ranking `P`

.

## Arguments

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

## Details

Note that the returned `mid_point`

is not the same as the expected
rank, for instance computed with exact_rank_prob.
It is simply the average of `min_rank`

and `max_rank`

. For exact rank probabilities
use exact_rank_prob.