These multidimensional scaling commands seek to preserve some notions of the geometric structure of the data within the reduced dimension representation. The points which lie close to each other in the input space will appear similarly close in the output space. These two commands use different methods for preserving the intrinsic structure of the data. Classical scaling tries to map data points in optimal fashion to the output space by using a principal component analysis. The Sammon's mapping maps data points to the output space by minimizing the distance difference between data points in the input and output space.
Example (ex5.13): The Sammon's mapping and the classical scaling.
... NDA> prepro -d boston -dout preboston -e -n NDA> somtr -d preboston -sout somboston -l 5 -cout cluboston # pick weights NDA> psl -s somboston -dout grid3 -l 3 -wout w3 # sammon mapping NDA> sammon -dinit grid3 -d w3 -dout out3 -imax 30 -eps 0.01 -ef virhe # setting transformed values for SOM NDA> ssl -s somboston -sset out3 -sout trans -l 3 # the same for the classical scaling NDA> classical -d w3 -dout class_out -dim 2 NDA> ssl -s somboston -sset class_out -sout class_weights -l 3 ...
