Re: [boost] [Review] Review of the Accumulators library begins today Jan 29

From: Hans Meine (meine_at_[hidden])
Date: 2007-02-01 07:36:41

On Wednesday, 31. January 2007 22:54, Matthias Troyer wrote:
> > Which accumulators would then have a non-trivial "combine" method?
>
> There are two types of accumulators that I can think of immediately:

Thanks for your answer, Matthias; I already suspected that you had some 
accumulators in mind which I don't know, thanks for giving examples. (I will 
have to look them up somewhere.)

> 1. approximate median and quantile estimators such as the p^2 methods
> cannot be combined but are very important for some applications
>
> 2. accumulators for correlates samples, e.g. autocorrelation
> estimators, or jackknife-bins cannot easily be combined. Instead of
> just merging the results one has to store the results from the
> individual accumulator_sets separately and combine them only in the
> final evaluations. Please keep in mind that correlated samples are
> very common.
>
> For 1. there is simply no way, and that is just it - one might either
> have to make this cause a compile-time error or drop the median and
> quantile estimators when combining.

I'd say that a compile-time error would be perfectly OK.  It's just that 
having a method for combining accumulators would open your library up to many 
more applications.  (E.g., in my case I would be interested in using it for 
image analysis, where I am using sort of accumulators for measuring 
properties of image regions, which are eventually merged.)

> For 2. the problem is that 
> combined accumulator sets need a different data structure than
> individual ones.

I would be very happy if you found a way to integrate a simple way for 
combining soon, and postpone a solution of that latter problem.

Right now, I don't think it would be impractical to require the user of your 
library to specify in advance that additional data structures shall be 
maintained in case he/she wants to combine accumulators later.

Ciao, /  /
     /--/
    /  / ANS