Add rapidity methods #9
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Add methods that return the true rapidity of LorentzVectors (E, p) these are defined for both cartesian and cylindrical cases as rap() Add methods for the square of mass and the square of momentum as these can be useful for more specialist calculations (but not exported)
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src/cartesian.jl
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| mass(lv::LorentzVector) = sqrt(dot(lv, lv)) | ||
| pt(lv::LorentzVector) = sqrt(muladd(lv.x, lv.x, lv.y^2)) | ||
| mass2(lv::LorentzVector) = dot(lv, lv) | ||
| mass(lv::LorentzVector) = mass2(lv) < 0.0 ? sqrt(-mass2(lv)) : sqrt(mass2(lv)) |
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is this negative mass trick universal? what's ROOT's Math::LorentzVector behavior on this
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ROOT adopts this convention for space-like 4-vectors, so that's some precedent
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I'm trying to think if we should err on the side of not silently produce wrong results
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Depends what one thinks of as being wrong. Negative mass is not ambiguous - but it may be surprising. I'm ok with rolling this back.
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Yeah, I guess I mean if we error, it's trivial for user to do what they want. But not the other way, they may silently get wrong results
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I checked in the Python Vector package and it also conforms to this behaviour:
In [1]: import vector
In [2]: ep_vec = vector.obj(x=8.1, y=2.2, z=3.3, E=4.4)
In [3]: ep_vec.mass
Out[3]: -7.87273777030583And I found I missed a - sign on the mass method, oops! Fixed in incoming commit.
This is the same method name as ScikitHEP's Vector package Add a note that we adopt the ROOT convention of returning a negative mass for space-like 4-vectors
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And add test for same
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Go ahead and merge this when you're ready! |
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Thanks @Moelf - merge early, merge often! Can we foresee a new release that can be a proper dependency for JetReconstruction.jl? |
Add methods that return the true rapidity of
LorentzVectors (E, p)these are defined for both cartesian and cylindrical cases asrap()rapidity().Add methods for the square of mass and the square of momentum (
mass2,pt2) as these can be useful for more specialist calculations (but not exported).