eigenvals.twinspan: Eigenvalues of twinspan Divisions

In jarioksa/twinspan: Two-Way Indicator Species Analysis

Eigenvalues of twinspan Divisions

Description

Function returns the eigenvalues of twinspan divisions.

Usage

## S3 method for class 'twinspan'
eigenvals(x, what = c("quadrat", "species"), ...)

Arguments

x	twinspan result object.
what	Return eigenvalues of "quadrat" or "species" divisions.
...	Other arguments (ignored).

Details

The eigenvalues are for the first correspondence analysis axis of downweighted pseudospecies data (see twinsform). The eigenvalues are not evaluated for final groups which are not divided further, nor if the analysis had terminated in a mother class. This leaves zeros in the vector of eigenvalues.

The eigenvalues are not additive and each is based on slightly different data due to downweighting (see twinsform) and all come from the first axis of respective analysis. They may have a relation to the magnitude of differences in division, but there is no information on the total Chi-square nor on its reduction in division: the eigenvalues only describe the strength of the axis used as a device of division. Neither can eigenvalues for quadrats and species compared: data for species clustering are constructed in a completely different way than data for quadrat classification.

Eigenvalues are in general not decreasing, but they can increase when divisions proceed. Function as.dendrogram.twinspan can try to use division eigenvalues as dendrogram heights, but the resulting trees often have inversions and look messy or even unreadable.

Value

Vector of eigenvalues ordered by division number, with zero for divisions that were not evaluated (terminal groups, division terminated in earlier steps).

See Also

eigenvals in vegan. summary.twinspan displays the eigenvalues numerically, and they can be used in as.dendrogram.twinspan.

Examples

data(ahti)
tw <- twinspan(ahti)
eigenvals(tw)

jarioksa/twinspan documentation built on Nov. 23, 2024, 2:49 p.m.