The quality function computes several quality criteria for the result of a SOM algorithm.

quality(sommap, quality.type, ...)

## Arguments

sommap A somRes object (see trainSOM for details). The quality type to compute. Two types are implemented: quantization and topographic. The output of the function is one of those or both of them using the option "all". Default value is the latter. Not used.

## Value

The quality function returns either a numeric value (if only one type is computed) or a list a numeric values (if all types are computed).

The quantization error calculates the mean squared euclidean distance between the sample vectors and their respective cluster prototypes. It is a decreasing function of the size of the map.

The topographic error is the simplest of the topology preservation measure: it calculates the ratio of sample vectors for which the second best matching unit is not in the direct neighborhood of the best matching unit.

## References

Polzlbauer G. (2004) Survey and comparison of quality measures for self-organizing maps. In: Proceedings of the Fifth Workshop on Data Analysis (WDA'04), Paralic, J., Polzlbauer, G., Rauber, A. (eds) Sliezsky dom, Vysoke Tatry, Slovakia: Elfa Academic Press, 67-82.

trainSOM, plot.somRes

## Examples

my.som <- trainSOM(x.data=iris[,1:4])
quality(my.som, quality.type="all")#> $topographic #> [1] 0.1933333 #> #>$quantization
#> [1] 0.9992276
#> quality(my.som, quality.type="topographic")#> [1] 0.1933333