Approaches to asymmetric multidimensional scaling with external information

In this paper some possible approaches to asymmetric multidimensional scaling with external information are presented to analyze graphically asymmetric proximity matrices. In particular, a proposal to incorporate external information in biplot method is provided. The methods considered allow joint or separate analyzes of symmetry and skew-symmetry. A final application to Morse code data is performed to emphasize advantages and shortcomings of the different methods proposed