[Rivet] [Rivet-svn] rivet: 4mom shouldnt be pointers cos they get reordered behind t...

[Jonathan Butterworth]

The functions which act on the vector of constituents reorder them...
e.g. constituentLepton() which uses the isChargedLepton function.

I agree it should not be possible for the user to do this, because the 
analysis code looks sensible and it was a bugger to track down...

On 02/03/2018 17:03, Andy Buckley wrote:
> This is a bit odd, because after application the projection should be a
> const reference -- not something that /can/ be reordered. Unless we're
> using mutable internally... which is possible, but I thought we called
> the sorting earlier. If it's possible for particle-list elements to be
> re-ordered after project(), breaking references/pointers exposed to user
> code, then we definitely need to fix that. Is that what was happening
> here, Jon?
>
> Andy
>
> *Dr Andy Buckley, Lecturer / Royal Society University Research Fellow*
> Particle Physics Experiment Group, University of Glasgow
> 	
>
> On Mar 1 2018, at 6:34 pm, David Grellscheid
> <david.grellscheid at durham.ac.uk> wrote:
>
>
>     Hi Jon,
>
>     Great find! Thanks! We've been looking at the return values of the
>     finders before, and this clearly demonstrates that they have very
>     delicate semantics right now with ordering.
>     We'll need to look at this properly, it's not the job of the
>     analysis authors to get this right.
>
>     See you,
>
>     David
>
>
>
>     On 1 March 2018 18:15:01 GMT, Rivet Mercurial
>     <rivet at projects.hepforge.org> wrote:
>
>         details: https://rivet.hepforge.org/hg/rivet/rev/ce40a6dcf214
>         branches: release-2-6-x
>         changeset: 6246:ce40a6dcf214
>         user: Jon Butterworth <j.butterworth at cern.ch>
>         date: Wed Feb 28 23:10:34 2018 +0100
>         description:
>         4mom shouldnt be pointers cos they get reordered behind the
>         scenes and
>         mT is then always zero.
>
>         diffs (20 lines):
>
>         --- a/analyses/pluginCMS/CMS_2016_I1491953.cc Tue Feb 27
>         22:34:33 2018
>         +0000
>         +++ b/analyses/pluginCMS/CMS_2016_I1491953.cc Wed Feb 28
>         23:10:34 2018
>         +0100
>         @@ -107,9 +107,14 @@
>         const WFinder& wfinder_mu = applyProjection<WFinder>(event,
>         "WFinder_mu");
>         if (wfinder_mu.bosons().size() != 1) vetoEvent;
>
>         - const FourMomentum& lepton0 =
>         wfinder_mu.constituentLeptons()[0].momentum();
>         - const FourMomentum& neutrino =
>         wfinder_mu.constituentNeutrinos()[0].momentum();
>         - double WmT = sqrt( 2 * lepton0.pT() * neutrino.pT() * (1 -
>         cos(deltaPhi(lepton0, neutrino))) );
>         + //const FourMomentum& lepton0 =
>         wfinder_mu.constituentLeptons()[0].momentum();
>         + //const FourMomentum& neutrino =
>         wfinder_mu.constituentNeutrinos()[0].momentum();
>         + //double WmT = sqrt( 2 * lepton0.pT() * neutrino.pT() * (1 -
>         cos(deltaPhi(lepton0, neutrino))) );
>         +
>         + const FourMomentum lepton0 =
>         wfinder_mu.constituentLepton().momentum();
>         + const FourMomentum neutrino =
>         wfinder_mu.constituentNeutrino().momentum();
>         + double WmT = wfinder_mu.mT();
>         +
>         if (WmT < 50.0*GeV) vetoEvent;
>         if (lepton0.abseta() > 2.1 || lepton0.pT() < 25.0*GeV) vetoEvent;
>
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-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Prof. Jonathan Butterworth,              http://www.hep.ucl.ac.uk/~jmb/
Head, Physics and Astronomy Department            Tel: +44 20 7679 3444
University College London                 Gower St, London WC1E 6BT, UK
ATLAS, CERN                                       Tel: +41 22 76  72340
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