unstable PS point detected

Asked by Wojciech Kotlarski

Dear MG/aMC@NLO experts,

I was testing generation of

p p > mu+ mu- [QCD] @0 ; p p > mu+ mu- j [QCD] @1 ; p p > mu+ mu- j j [QCD] @2

for the UNLOPS matching/merging. Run goes fine but it end with a message

Number of loop ME evaluations (by MadLoop): 3134633
    Stability unknown: 0
    Stable PS point: 3133011
    Unstable PS point (and rescued): 1618
    Unstable PS point (and not rescued): 4
    Only double precision used: 3133011
    Quadruple precision used: 1622
    Initialization phase-space points: 1176
    Reduction methods used:
      > CutTools (double precision) 3125616
      > IREGI 7395
      > CutTools (quadruple precision) 1618
      > Not identified (CTModeRun != -1) 4
  Total number of unstable PS point detected: 4 (0.00%)
    Maximum fraction of UPS points in channel mu+mu-_nlo_012/SubProcesses/P2_dxg_mupmumdxg/GF15 (0.04%)

The fraction of unstable PS point is negligible, but still I though it might be worthwhile to report it. Is this expected or is this a bug?


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MadGraph5_aMC@NLO Edit question
Valentin Hirschi Edit question
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Olivier Mattelaer (olivier-mattelaer) said :


Yes this is completely expected, all those rescued means that the problem were solved by using a slower method of computation.
(can be 100 times slower to compute than the normal method).
Valentin might be interested by the fact that you still have 4 point that are not rescued and set to zero.



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Wojciech Kotlarski (wojciech-kotlarski) said :

Dear Olivier,

Thanks a lot for looking into this and sorry for not being very precise. What I was worried about are precisely those 4 points you mentioned. The ones that weren't "fixed" by rescue/fallback system.


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