R: SOM-grid related functions

unit.distances {kohonen} | R Documentation

## SOM-grid related functions

### Description

Function `somgrid` (modified from the version in the class package) sets up a grid of units, of a specified size and topology. Distances between grid units are calculated by function `unit.distances`.

### Usage

    somgrid(xdim = 8, ydim = 6, topo = c("rectangular", "hexagonal"),
            neighbourhood.fct = c("bubble", "gaussian"), toroidal = FALSE)
    unit.distances(grid, toroidal)

### Arguments

`xdim, ydim` | dimensions of the grid.
`topo` | choose between a hexagonal or rectangular topology.
`neighbourhood.fct` | choose between bubble and gaussian neighbourhoods when training a SOM.
`toroidal` | logical, whether the grid is toroidal or not. If not provided to the `unit.distances` function, the information in the `grid` object will be used.
`grid` | an object of class `somgrid`.

### Value

Function `somgrid` returns an object of class "somgrid", with elements `pts`, and the input arguments to the function.

Function `unit.distances` returns a (symmetrical) matrix containing distances. When `grid$n.hood` equals "circular", Euclidean distances are used; for `grid$n.hood` is "square" maximum distances. For toroidal maps (joined at the edges) distances are calculated for the shortest path.

### Author(s)

Ron Wehrens

### Examples

    mygrid <- somgrid(5, 5, "hexagonal")
    fakesom <- list(grid = mygrid)
    class(fakesom) <- "kohonen"

    par(mfrow = c(2,1))
    dists <- unit.distances(mygrid)
    plot(fakesom, type="property", property = dists[1,],
         main="Distances to unit 1", zlim=c(0,6),
         palette = rainbow, ncolors = 7)

    dists <- unit.distances(mygrid, toroidal=TRUE)
    plot(fakesom, type="property", property = dists[1,],
         main="Distances to unit 1 (toroidal)", zlim=c(0,6),
         palette = rainbow, ncolors = 7)

[Package kohonen version 3.0.4 Index]