Calculate or plot the minimum spanning tree (Gower and Ross 1969) of a distance matrix.

## Arguments

- distances
Either a matrix that can be interpreted as a distance matrix, or an object of class

`dist`

.- plot
Logical specifying whether to add the minimum spanning tree to an existing plot.

- x, y
Numeric vectors specifying the X and Y coordinates of each element in

`distances`

. Necessary only if`plot = TRUE`

.- ...
Additional parameters to send to

`[lines()]`

.- mst
Optional parameter specifying the minimum spanning tree in the format returned by

`MSTEdges()`

; if`NULL`

, calculated from`distances`

.

## Value

`MSTEdges()`

returns a matrix in which each row corresponds to an
edge of the minimum spanning tree, listed in non-decreasing order of length.
The two columns contain the indices of the entries in `distances`

that
each edge connects, with the lower value listed first.

`MSTLength()`

returns the length of the minimum spanning tree.

## References

Gower JC, Ross GJS (1969).
“Minimum spanning trees and single linkage cluster analysis.”
*Journal of the Royal Statistical Society. Series C (Applied Statistics)*, **18**(1), 54–64.
doi:10.2307/2346439
.

## See also

Slow implementation returning the association matrix of the minimum spanning
tree: `ape::mst()`

.

## Examples

```
# Corners of an almost-regular octahedron
points <- matrix(c(0, 0, 2, 2, 1.1, 1,
0, 2, 0, 2, 1, 1.1,
0, 0, 0, 0, 1, -1), 6)
distances <- dist(points)
mst <- MSTEdges(distances)
MSTLength(distances, mst)
#> [1] 8.496869
plot(points[, 1:2], ann = FALSE, asp = 1)
MSTEdges(distances, TRUE, x = points[, 1], y = points[, 2], lwd = 2)
```