# edges_coords: Compute ego/alter edge coordinates considering alter's size... In USCCANA/netdiffuseR: Analysis of Diffusion and Contagion Processes on Networks

## Description

Given a graph, vertices' positions and sizes, calculates the absolute positions of the endpoints of the edges considering the plot's aspect ratio.

## Usage

 ``` 1 2 3 4 5 6 7 8 9 10 11 12``` ```edges_coords( graph, toa, x, y, vertex_cex, undirected = TRUE, no_contemporary = TRUE, dev = as.numeric(c()), ran = as.numeric(c()), curved = as.logical(c()) ) ```

## Arguments

 `graph` A square matrix of size n. Adjacency matrix. `toa` Integer vector of size n. Times of adoption. `x` Numeric vector of size n. x-coordinta of vertices. `y` Numeric vector of size n. y-coordinta of vertices. `vertex_cex` Numeric vector of size n. Vertices' sizes in terms of the x-axis (see `symbols`). `undirected` Logical scalar. Whether the graph is undirected or not. `no_contemporary` Logical scalar. Whether to return (compute) edges' coordiantes for vertices with the same time of adoption (see details). `dev` Numeric vector of size 2. Height and width of the device (see details). `ran` Numeric vector of size 2. Range of the x and y axis (see details). `curved` Logical vector.

## Details

In order to make the plot's visualization more appealing, this function provides a straight forward way of computing the tips of the edges considering the aspect ratio of the axes range. In particular, the following corrections are made at the moment of calculating the egdes coords:

• Instead of using the actual distance between ego and alter, a relative one is calculated as follows

d'=sqrt[(x0-x1)^2 + (y0'-y1')^2]

where yi' = yi * [max(x) - min(x)]/[max(y) - min(y)]

• Then, for the relative elevation angle, `alpha`, the relative distance d' is used, α' = acos[ (x0 - x1)/d' ]

• Finally, the edge's endpoint's (alter) coordinates are computed as follows:

x1' = x1 + cos(α') * v1

y1' = y1 -+ sin(α')*[max(y) - min(y)]/[max(x) - min(x)]

Where v1 is alter's size in terms of the x-axis, and the sign of the second term in y1' is negative iff y0<y1.

The same process (with sign inverted) is applied to the edge starting piont. The resulting values, x1',y1' can be used with the function `arrows`. This is the workhorse function used in `plot_threshold`.

The `dev` argument provides a reference to rescale the plot accordingly to the device, and former, considering the size of the margins as well (this can be easily fetched via `par("pin")`, plot area in inches).

On the other hand, `ran` provides a reference for the adjustment according to the range of the data, this is `range(x) - range(x)` and `range(y) - range(y)` respectively.

## Value

A numeric matrix of size m * 5 with the following columns:

 `x0, y0` Edge origin `x1, y1` Edge target `alpha` Relative angle between `(x0,y0)` and `(x1,y1)` in terms of radians

With m as the number of resulting edges.

## Examples

 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25``` ```# -------------------------------------------------------------------------- data(medInnovationsDiffNet) library(sna) # Computing coordinates set.seed(79) coords <- sna::gplot(as.matrix(medInnovationsDiffNet\$graph[])) # Getting edge coordinates vcex <- rep(1.5, nnodes(medInnovationsDiffNet)) ecoords <- edges_coords( medInnovationsDiffNet\$graph[], diffnet.toa(medInnovationsDiffNet), x = coords[,1], y = coords[,2], vertex_cex = vcex, dev = par("pin") ) ecoords <- as.data.frame(ecoords) # Plotting symbols(coords[,1], coords[,2], circles=vcex, inches=FALSE, xaxs="i", yaxs="i") with(ecoords, arrows(x0,y0,x1,y1, length=.1)) ```

USCCANA/netdiffuseR documentation built on Feb. 21, 2020, 8:01 p.m.