scikit-learn/scikit-learn — pull request #983 by GaelVaroquaux (2012-07-26 07:23:44+00:00)
Title: WIP: Faster ward

The main contribution of the PR is to implement a variant of the Ward strategy that gives speed ups for a large number of clusters. The speed up get really important when the number of clusters is on the order of magnitude of the sample size, for very sparse matrices. A typical application is light data decimation, as in building super-voxels on image. For brain images (n_samples = 50000) for 10000 clusters, the speed up is approximately a factor of 3.