I am using a calculation of the Variance-Covariance matrix in a program I wrote (for Principal Component Analysis), and am wondering what the complexity of it is. While obviously the Eigenvector decomposition is causing the largest performance hit, I am wondering how much of that hit is caused by the Covariance Matrix computation.
The asymptotic running time I estimate it to use is $O(N\cdot n^2)$ using a naive algorithm, because it has to take the means of all the data of size $N$ and then has to do it for every dimension (where $n$ is the number of dimensions) in a nested iteration, and thus producing a $n^2$ size matrix.
Is my assumption correct, or if not what is the asymptotic complexity?
