Anna Arutyunova, A. Großwendt, Heiko Röglin, Melanie Schmidt, Julian Wargalla
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引用次数: 1
Abstract
In a hierarchical clustering problem the task is to compute a series of mutually compatible clusterings of a finite metric space $$(P,{{\,\textrm{dist}\,}})$$ ( P , dist ) . Starting with the clustering where every point forms its own cluster, one iteratively merges two clusters until only one cluster remains. Complete linkage is a well-known and popular algorithm to compute such clusterings: in every step it merges the two clusters whose union has the smallest radius (or diameter) among all currently possible merges. We prove that the radius (or diameter) of every k -clustering computed by complete linkage is at most by factor O ( k ) (or $$O(k^{\ln (3)/\ln (2)})=O(k^{1{.}59})$$ O ( k ln ( 3 ) / ln ( 2 ) ) = O ( k 1.59 ) ) worse than an optimal k -clustering minimizing the radius (or diameter). Furthermore we give a negative answer to the question proposed by Dasgupta and Long (J Comput Syst Sci 70(4):555–569, 2005. https://doi.org/10.1016/j.jcss.2004.10.006 ), who show a lower bound of $$\Omega (\log (k))$$ Ω ( log ( k ) ) and ask if the approximation guarantee is in fact $$\Theta (\log (k))$$ Θ ( log ( k ) ) . We present instances where complete linkage performs poorly in the sense that the k -clustering computed by complete linkage is off by a factor of $$\Omega (k)$$ Ω ( k ) from an optimal solution for radius and diameter. We conclude that in general metric spaces complete linkage does not perform asymptotically better than single linkage, merging the two clusters with smallest inter-cluster distance, for which we prove an approximation guarantee of O ( k ).
SpinMaterials Science-Electronic, Optical and Magnetic Materials
CiteScore
2.10
自引率
11.10%
发文量
34
期刊介绍:
Spin electronics encompasses a multidisciplinary research effort involving magnetism, semiconductor electronics, materials science, chemistry and biology. SPIN aims to provide a forum for the presentation of research and review articles of interest to all researchers in the field.
The scope of the journal includes (but is not necessarily limited to) the following topics:
*Materials:
-Metals
-Heusler compounds
-Complex oxides: antiferromagnetic, ferromagnetic
-Dilute magnetic semiconductors
-Dilute magnetic oxides
-High performance and emerging magnetic materials
*Semiconductor electronics
*Nanodevices:
-Fabrication
-Characterization
*Spin injection
*Spin transport
*Spin transfer torque
*Spin torque oscillators
*Electrical control of magnetic properties
*Organic spintronics
*Optical phenomena and optoelectronic spin manipulation
*Applications and devices:
-Novel memories and logic devices
-Lab-on-a-chip
-Others
*Fundamental and interdisciplinary studies:
-Spin in low dimensional system
-Spin in medical sciences
-Spin in other fields
-Computational materials discovery