This vignette describes the importance of indirect relations on
networks, how they are used in centrality indices and how they are
implemented in the `netrankr`

package.

A one-mode network can be described as a *dyadic variable*
\(x\in \mathcal{W}^\mathcal{D}\), where
\(\mathcal{W}\) is the value range of
the network (in the simple case of unweighted networks \(\mathcal{W}=\{0,1\}\)) and \(\mathcal{D}=\mathcal{N}\times\mathcal{N}\)
describes the dyadic domain of actors \(\mathcal{N}\).

Observed presence or absence of ties (the value range is binary) is
usually not the relation of interest for network analytic tasks.
Instead, mostly implicitly, relations are *transformed* into a
new set of *indirect* relations on the basis of the
*observed* relations. As an example, consider (shortest path)
distances in the underlying graph. While they are fairly easy to derive
from an observed network of contacts, it is impossible for actors in a
network to answer the question “How far away are you from others you are
not connected with?”. We denote generic transformed networks from an
observed network \(x\) as \(\tau(x)\).

With this notion of indirect relations, we can express centrality
indices in a common framework as \[
c_\tau(i)=\sum\limits_{t \in \mathcal{N}} \tau(x)_{it}
\] Degree and closeness centrality, for instance, can be obtained
by setting \(\tau=id\) and \(\tau=dist\), respectively. Others need
several additional specifications which can be found in Brandes (2016) or
Schoch & Brandes
(2016).

With this framework, we can characterize centrality indices as
degree-like measures in a suitably transformed network \(\tau(x)\).

`netrankr`

packageThe `netrankr`

package implements a great variety of
indirect relations that are (or could be) used for centrality related
considerations in a network. All indirect relations can be computed with
the `indirect_relations()`

function, by specifying the
`type`

parameter.

```
## This graph was created by an old(er) igraph version.
## Call upgrade_graph() on it to use with the current igraph version
## For now we convert it on the fly...
```

`## Warning in indirect_relations(g, type = "identity"): type="identity" is deprecated. Using "adjacency" instead.`

```
#shortest path distances
D <- indirect_relations(g,type="dist_sp")
#dyadic dependencies (as used in betweenness centrality)
B <- indirect_relations(g,type = "depend_sp")
#resistance distance (as used in information centrality)
R <- indirect_relations(g,type="dist_resist")
#Logarithmic forest distance (parametrized family of distances)
LF <- indirect_relations(g, type = "dist_lf",lfparam = 1)
#Walk distance (parametrized family of distances)
WD <- indirect_relations(g, type = "dist_walk",dwparam = 0.001)
#Random walk distance
WD <- indirect_relations(g, type = "dist_rwalk")
#See ?indirect_relations for further options
```

The function takes an additional parameter `FUN`

which can
be used to pass a function to further transform relations. The main use
is to obtain indirect relations based on walk counts.

```
#count the limit proportion of walks (used for eigenvector centrality)
W <- indirect_relations(g,type = "walks",FUN = walks_limit_prop)
#count the number of walks of arbitrary length between nodes, weighted by
#the inverse factorial of their length (used for subgraph centrality)
S <- indirect_relations(g,type = "walks",FUN = walks_exp)
```

Additional parameters can also be passed to calculate parameterized versions of relations.

To view all predefined transformation functions see
`?transform_relations`

. The predefined functions follow the
naming scheme `<relation>_<transformation>`

. The
functions `dist_`

are thus only meaningful fordistance type
relations such as `type="dist_sp"`

or
`type="dist_resist"`

. Equivalently, `walks_`

for
`type="walks"`

. The predefined functions are not exhaustive
and just constitute the most common transformations. It is, however,
straightforward to pass your own transformation function.

```
dist_integration <- function(x){
x <- 1 - (x - 1)/max(x)
}
D <- indirect_relations(g,type="dist_sp",FUN=dist_integration)
```

The function `dist_integration()`

computes \[
\tau(x)_{ij}=1-\frac{dist(i,j)-1}{max_{i,j}\; dist(i,j)}
\] which is used in the centrality index *integration*
defined by Valente and Foreman
(1998)

The computed relations CAN be used to build centrality indices
(e.g. with the provided Rstudio `index_builder()`

), but also
to derive partial rankings with `positional_dominance()`

.
Consult the respective vignette
for help.