dc.contributor.author | Fieldsend, Jonathan E. | |
dc.date.accessioned | 2013-07-08T13:03:38Z | |
dc.date.issued | 2005 | |
dc.description.abstract | When estimating how much better a classifier is than random allocation in Q-class ROC analysis, we need to sample from a particular region of the unit hypercube: specifically the region, in the unit hypercube, which lies between the Q − 1 simplex in
Q(Q − 1) space and the origin.
This report introduces a fast method for randomly sampling this volume, and is compared to rejection sampling of uniform draws from the unit hypercube. The new method is based on sampling from a Dirichlet distribution and shifting these samples using a draw from the Uniform distribution. We show that this method generates random samples within the volume at a probability ≈ 1/(Q(Q − 1)), as opposed to ≈ (Q − 1)Q(Q − 1) /(Q(Q − 1))! for rejection sampling from the unit hypercube.
The vast reduction in rejection rates of this method means comparing classifiers in a Q-class ROC framework is now feasible, even for large Q. | en_GB |
dc.description.sponsorship | Department of Computer Science, University of Exeter | en_GB |
dc.identifier.citation | Report No. 421, Department of Computer Science, University of Exeter | en_GB |
dc.identifier.uri | http://hdl.handle.net/10871/11564 | |
dc.language.iso | en | en_GB |
dc.publisher | University of Exeter | en_GB |
dc.title | A short note on the efficient random sampling of the multi-dimensional pyramid between a simplex and the origin lying in the unit hypercube | en_GB |
dc.type | Report | en_GB |
dc.date.available | 2013-07-08T13:03:38Z | |
exeter.confidential | false | |
dc.description | Copyright © 2005 University of Exeter | en_GB |