Editing Nonlinear dimensionality reduction (section)

=== Sammon's mapping ===

[[Sammon's mapping]] is one of the first and most popular NLDR techniques.

[[File:SOMsPCA.PNG|thumb|200px|left|Approximation of a principal curve by one-dimensional [[Self-organizing map|SOM]] (a [[broken line]] with red squares, 20 nodes). The first [[Principal component analysis|principal component]] is presented by a blue straight line. Data points are the small grey circles. For PCA, the [[Fraction of variance unexplained]] in this example is 23.23%, for SOM it is 6.86%.<ref>The illustration is prepared using free software: {{cite web |first=E.M. |last=Mirkes |url=http://www.math.le.ac.uk/people/ag153/homepage/PCA_SOM/PCA_SOM.html |title=Principal Component Analysis and Self-Organizing Maps: applet |publisher=University of Leicester |date=2011}}</ref>]]