## Mathematics

## General Scientific Interest

InnoCentive - where the world innovates - www.innocentive.com

## K-means & correlation distance

Here's a useful observation related to the use of K-means together with the Pearson correlation distance (© Alex).

The standard K-means update step, where you update the cluster centers by taking the means of the corresponding points is technically not very appropriate in the case of the correlation distance *d(x, y) = 1 - corr(x, y)*. The proper step would be to take the *sum of the *normalized* points* as the new cluster center:

*c = sum _{i}(x_{i}/|x_{i}|)*

## A Brief Introduction to Matrix Algebra

I made up a short guide on the basics of matrix algebra for the recent pattern analysis course to kinda help the catch-uppers.

Despite the fact that it did not seem to help a lot (it's probably too compressed for a beginner and too obvious for the one who knows), I still decided to make it into a more-or-less complete document, which maybe someday end up being useful.

The good point about it is that it summarizes about pretty much **all** of linear algebra that I, personally, know and find useful.

The PDF is available here.