[Rivet] hopefully quick Rivet assertion question

[Andy Buckley]

On 09/12/13 13:47, Caterina Doglioni wrote:
> Hi Andy,
> 
> I have a possibly strange thing happening to a Rivet code that I'm using
> (Cigdem in cc) - if it's a bug I'll chase it up through the official
> channel, but if this is not the case and I'm doing something wrong,
> emailing just you will spare my silly error being exposed to a wider
> audience :). Some snippets:
> 
> leadjets[0] and [1] are 4-momenta that I get from:
> 
> const Jets jets = applyProjection<JetAlg>(event, "Jets").jetsByPt(100*GeV);
> 
> out of a Pythia8+Sacrifice jetty final state. However, sometimes (e.g.
> after 300 events in one of the runs) one of the following lines:
> 
> delta_phi[j12] = Rivet::deltaPhi(leadjets[0], leadjets[1]);
> delta_phi[j13] = Rivet::deltaPhi(leadjets[1], leadjets[3]);
> delta_phi[j23] = Rivet::deltaPhi(leadjets[2], leadjets[3]);
> 
> crashes my entire code with:
> 
> python:
> /afs/cern.ch/user/d/doglioni/Work/ThreeJet_Rivet2/local/include/Rivet/Math/MathUtils.hh:419:
> double Rivet::_mapAngleM2PITo2Pi(double): Assertion `rtn >= -TWOPI &&
> rtn <= TWOPI' failed.
> Aborted (core dumped)
> 
> I've checked that leadjets[0] and [1] are sane, and that their phi value
> is from 0 to 2pi, but I haven't managed to track down where things go
> wrong because this is unfortunately not always happening at the same
> place! One instance of incriminated jets is here:
> 
> phi j1:0.387629
> phi j2:3.61709
> phi j3:1.82318
> python:
> /afs/cern.ch/user/d/doglioni/Work/ThreeJet_Rivet2/local/include/Rivet/Math/MathUtils.hh:419:
> double Rivet::_mapAngleM2PITo2Pi(double): Assertion `rtn >= -TWOPI &&
> rtn <= TWOPI' failed.
> 
> If you can spot the problem without effort from your side I'll be happy
> to hear it - but let me know if you prefer this to go into official
> channels.

Hi Caterina, Cigdem... and I've CC'd the Rivet list,

That is very strange. a) I thought that we had already knocked all the
wrinkles out of those deltaPhi asserts, and b) those phi values are
already within the -2pi..2pi range and so nothing should happen at all!
The relevant code is this:

https://rivet.hepforge.org/trac/browser/include/Rivet/Math/MathUtils.hh#L412

and I implemented a tiny test program (attached) to run the same logic
and assert on the values you supplied (TWOPI = 2*M_PI in
https://rivet.hepforge.org/trac/browser/include/Rivet/Math/MathHeader.hh#L50).
Unsurprisingly it's fine:

andy at duality:~/tmp/testfmod$ g++ testfmod.cc -o testfmod
andy at duality:~/tmp/testfmod$ ./testfmod
0.387629 -> 0.387629 = 0.123386*PI
3.61709 -> 3.61709 = 1.15136*PI
1.82318 -> 1.82318 = 0.580336*PI

Does anyone else know what might be going on here? Do you know which
specific phi value is causing the trouble, Cate? If you could put the
analysis code and a HepMC dump of the events (300 events in ASCII is not
enormous) somewhere ~public, e.g. your AFS public dir then I can look in
more detail.

A workaround for now is to add CPPFLAGS=-DNDEBUG to your configure or
make command line before building Rivet (you are using a private build,
yes?). This will disable the assert. I actually thought that the asserts
were only active when -g was used, but it turns out that that only
controls the debug symbols and that assert disabling requires the NDEBUG
#define, cf.
http://stackoverflow.com/questions/5354314/how-to-completely-disable-assertion

Cheers,
Andy

-- 
Dr Andy Buckley, Royal Society University Research Fellow
Particle Physics Expt Group, University of Glasgow / PH Dept, CERN
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