Statistics and Computing

, Volume 29, Issue 2, pp 391–414 | Cite as

Minimum spectral connectivity projection pursuit

Divisive clustering using optimal projections for spectral clustering
  • David P. HofmeyrEmail author
  • Nicos G. Pavlidis
  • Idris A. Eckley


We study the problem of determining the optimal low-dimensional projection for maximising the separability of a binary partition of an unlabelled dataset, as measured by spectral graph theory. This is achieved by finding projections which minimise the second eigenvalue of the graph Laplacian of the projected data, which corresponds to a non-convex, non-smooth optimisation problem. We show that the optimal univariate projection based on spectral connectivity converges to the vector normal to the maximum margin hyperplane through the data, as the scaling parameter is reduced to zero. This establishes a connection between connectivity as measured by spectral graph theory and maximal Euclidean separation. The computational cost associated with each eigen problem is quadratic in the number of data. To mitigate this issue, we propose an approximation method using microclusters with provable approximation error bounds. Combining multiple binary partitions within a divisive hierarchical model allows us to construct clustering solutions admitting clusters with varying scales and lying within different subspaces. We evaluate the performance of the proposed method on a large collection of benchmark datasets and find that it compares favourably with existing methods for projection pursuit and dimension reduction for data clustering. Applying the proposed approach for a decreasing sequence of scaling parameters allows us to obtain large margin clustering solutions, which are found to be competitive with those from dedicated maximum margin clustering algorithms.


Spectral clustering Dimension reduction Projection pursuit Maximum margin 



The authors would like to thank the anonymous reviewers for their insightful recommendations, which helped improve the quality of the paper. They would also like to thank Dr. Teemu Roos for his valuable comments on this work. Finally, they are very grateful to Dr. Kai Zhang for providing code to implement the iSVR algorithm.

Supplementary material


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© Springer Science+Business Media, LLC, part of Springer Nature 2018

Authors and Affiliations

  • David P. Hofmeyr
    • 1
    Email author
  • Nicos G. Pavlidis
    • 2
  • Idris A. Eckley
    • 3
  1. 1.Department of Statistics and Actuarial ScienceStellenbosch UniversityStellenboschSouth Africa
  2. 2.Department of Management ScienceLancaster UniversityLancasterUK
  3. 3.Department of Mathematics and StatisticsLancaster UniversityLancasterUK

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