[Rivet] [Yoda] YODA development

[Ben Waugh]

Hi Andy,

On 02/11/09 15:26, Andy Buckley wrote:
>> I think we agree, don't we, that wherever N is a meaningful quantity
>> sum(w) is the appropriate way to calculate it?
>
> Good... I was still vacillating on that, and wasn't sure if you were
> disagreeing :D

[...]

> Yes, sounds good. But isn't that in contradiction with N = sum(w).
> Should we use N = #fills rather than sum(w) for the binomial/Poisson bin
> height errors? I think this is still okay from a repartitioning
> standpoint... and since the binomial/Poisson stats relate to a number of
> trials I can see this making sense... but a definitive reference would
> be nice.

To recap, I still think that:
  * bin height = sum(w)
  * error on bin height = sqrt(sum(w^2))
This follows intuitively from something like:
  w1(1+-1) + w2(1+-1) + ... wn(1+-1)
  = (w1 + w2 + ... + wn) +- sqrt(w1^2 + w2^2 + ... wn^2)
But yes, a definitive reference and/or a more rigorous derivation would 
be nice.

>>> Except where the observable itself is signed... hmm.
>>
>> Disagreed! I don't think the sign of the observable makes any difference.
>
> Okay, you're right. The problem here is that (A)EEC is implemented in
> Rivet by use of an extra signed term multiplying the generator event
> weight. If YODA is designed to do this properly, i.e. assuming that
> "weight" implies a statistically meaningful measure (i.e. which will be
>  >= 0 with asymptotic statistics), then the Rivet implementation(s) of
> (A)EEC will need to be updated not to abuse the weight.

I see. Yes, that could be seen as abuse!

> Thanks for the discussion, by the way --- I think this has been a really
> useful way to work out what YODA should be doing (and what ROOT, AIDA
> etc. should have been doing, too, so that we didn't have to have this
> discussion at all!)

My pleasure. It's good to have an excuse to think about these things 
again now that my stats knowledge is getting a bit rusty. When I get a 
chance I'll have to have a look and see what ROOT and AIDA have been 
doing. Are they really getting this wrong?

Cheers,
Ben

-- 
Dr Ben Waugh                                   Tel. +44 (0)20 7679 7223
Dept of Physics and Astronomy                  Internal: 37223
University College London
London WC1E 6BT