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From Al Chou <>
Subject Re: [math] Apples or Oranges
Date Mon, 16 Jun 2003 19:55:23 GMT
--- "Mark R. Diggory" <> wrote:
> Andreou Andreas wrote:
> > Mark, I would go for the latter approach (the one on the p.s.) cause 
> > it doesn't seem that complex to me...
> > Why not add a CachableUnivariateImpl class
> > that extends UnivariateImpl
> > and also keeps track in a cache the results of the getters (getMean, 
> > getKurtosis, e.t.c.).
> > In this way, whenever a new value is added, the cache will be cleared, 
> > and on calling the getters, each correspending statistic will be
> > recalculated.
> > If no new values have been added, this new subclass will just return 
> > the cached results... 
> Yes, I think this is a novel idea to explore in the future, its 
> difficult to draw the lines on what to store in it because at this time, 
> we are now calculating the mean/variance in addValue with Al's new 
> 2-pass algorithm, while the more complex kurt and skew calculations are 
> in the getter methods. But, I like the idea of it. I'm working on 2-pass 
> style algorithms for skew and kurt now. Which may unfortunately require 
> more calculation to occur in addValue than I want to see happening.

Before I say something more substantive about the original question, I just
want to shoot out a "huh?" about "my" "2-pass" algorithm.  I think of what I
submitted over the weekend as a 1-pass storage-less/updating algorithm.

I did mention that the corrected 2-pass algorithm had not yet been implemented
in StoreUnivariateImpl.


Albert Davidson Chou

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