[Rivet] ATLAS inclusive isolated diphoton analysis in Rivet

[Andy Buckley]

On 28/09/11 15:47, Hendrik Hoeth wrote:
> Hi Giovanni,
>
> I'm looking at the ATLAS_2011_S9120807 Rivet analysis for which you are
> listed as author, and I see these lines of code:
>
>    if( nDens%2 == 0 )
>      median = (ptDensities[b][nDens/2]+ptDensities[b][(nDens-2)/2])/2;
>    else
>      median = ptDensities[b][(nDens-1)/2];
>
> I'm not familiar with that analysis, but I guess you are trying to
> calculate a median here. Shouldn't it then be (nDens+2)/2 instead of
> (nDens-2)/2 in the first line?

Really? Let's say the array has 10 entries -- in that case Giovanni's 
median is the mean of the 5th and 6th entries. Since C(++) arrays are 
zero-based, that means myarray[4] = myarray[10/2 - 1] and myarray[5] = 
myarray[10/2 + 1 - 1] = myarray[10/2]. That's effectively what Giovanni 
has, it's just that the [num/2 - 1] is written as [(num-2)/2]... which I 
think makes the motivation a bit unclear but isn't wrong.

Or did I screw up? ;)

-- 
Dr Andy Buckley
SUPA Advanced Research Fellow
Particle Physics Experiment Group, University of Edinburgh

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