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).

- quality.type
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.

## Examples

```
my.som <- trainSOM(x.data = iris[,1:4])
quality(my.som, quality.type = "all")
#> $topographic
#> [1] 0.006666667
#>
#> $quantization
#> [1] 0.9992276
#>
quality(my.som, quality.type = "topographic")
#> [1] 0.006666667
```