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This paper linke to continuing research of the first author on codes in graphs [7–11]. Here codes are studied from the point of view of their computational complexity. It is shown that the problem of perfect code recognition is NP-complete even when resiricted to k-regular graphs (k≥4) or to 3-regular planar graphs. On the other hand in the case of trees and graphs of bounded tree-width an optimal...
It is shown that the problem of finding the minimum number of bracketing transfers in order to transform one bracketing to another bracketing is an NP-complete problem. This problem is related to problems on random walks, planar triangulations of convex polygons and to the problem of comparison of two (labeled) rooted trees. The latter problem is studied with the connection to cluster analysis. Finally,...
We explore hierarchical clustering methods in the plane within the context of visual separability by means of graphs of elliptical influence. A novel efficient method of visual hierarchical clustering is developed.