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From Phil Steitz <>
Subject Re: [math] Matrix subMatrix and mean methods
Date Sun, 03 Oct 2004 12:25:37 GMT
Kim van der Linde wrote:
> Hi Phil,
> I have been thinking for a few days on the Matrix classes.
> I think the Matrix class itself should contain all those methods that do 
> matrix calculations (add, subtract, multiply) that either a Matrix 
> themselfs or proporties of the Matrix (isSingular for example).

I agree.

  The mean
> methods (getRowMeans) etc are statistics done ON a matrix, and I think 
> they should be in a seperate class, maybe called MatrixStats. This 
> enables aso he option to add variances and SD's which are needed for 
> column mean resp mean-SD standardizations, to be used for example in PCA 
> calculations when a covariance resp. correlation matrix is used.

I agree here as well. Do you see use cases where you will want to start 
with a double[][] array, perform matrix operations on it (say some 
decomposition) and then run stats on the resulting matrix? Will it be too 
onerous to make copies of the double[][] at each stage?  If so, we need to 
think about access to the double[][].
> Is there the intention to add an EigenvalueDecomposition class to the 
> package? In that case, which algorithm is targeted to be used? Jacobi?

We have not discussed this. Feel free to add to the wish list and propose 
an algorithm. We also need to discuss how best to implement the strategy 
pattern for decompositions in general, as there will often be multiple 
algorithms to choose from.

> Cheers,
> Kim

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