Re: TLorentzVector

From: Nick van Eijndhoven (Nick@phys.uu.nl)
Date: Wed Nov 03 1999 - 10:03:59 MET


Hi Victor,
Maybe I am missing a point here, but the dotproduct you mention
below has to my opinion no physical meaning and as such I would
say should not be supported or at least the user should receive a
warning message that he/she is doing nonsense.
However, as I said I may be missing a point here and then I am
saying nonsense.

                                            Cheers,
                                             Nick.  

Victor Perevoztchikov wrote:
> 
> Hi Peter,
> > but not between 3 and 4 Vectors. What would you expect to get as result
> > of the scalar product between a 3-vector and a 4-vector ...
> 
> It seems me it is evident. It must be used all possible information.
> Si in the case of scalar product between a 3-vector and a 4-vector
>  must give scalar 3*3
> 
> Victor
> 
> Peter Malzacher wrote:
> >
> > Hi Martin, hi Pasha,
> >
> > > inline void TLorentzVector::SetPPhiThetaM(Double_t p,
> > >                                           Double_t phi,
> > >                                           Double_t theta,
> > >                                           Double_t m)
> > > {
> > >   // initialize vector with spherical coordinates
> > >   SetX(p * TMath::Cos(phi) * TMath::Sin(theta));
> > >   SetY(p * TMath::Sin(phi) * TMath::Sin(theta));
> > >   SetZ(p * TMath::Cos(theta));
> > >   fE = TMath::Sqrt(p*p + m*m);
> > > }
> >
> > I can implement setter functions in spherical coordinates,
> > but I prefer to name it SetRhoPhiTheta.
> >
> > > I'd like to raise once again the issue of the relationship between
> > > TLorentzVector and TVector3. I'm coming back to it every time I realize
> > > that I can't do something as efficient and convenient as I'd like to.
> >
> > As announced some months ago we will cleanup the current implementation
> > of TLorentzVecter when the corresponding classes of ZOOM and CLHEP will
> > be merged. We will try to stay as close to their implementation as
> > possible.
> > The problem with inheriting from TVector3 occurs when one
> > uses methods which meke sense between 3-Vectors or between 4-Vectors
> > but not between 3 and 4 Vectors. What would you expect to get as result
> > of the scalar product between a 3-vector and a 4-vector ...
> > Therefore I think it is better to be explicit and get the 3-Vector
> > component
> > of a 4-Vector when you need it. Ok its slightly more inconvenient to
> > type,
> > but if one gets a const reference to an internal 3-Vector its as
> > efficient as
> > inheritance.
> >
> > Peter
> 
> --
> Victor M. Perevoztchikov   perev@bnl.gov  perev@vxcern.cern.ch
> Brookhaven National Laboratory MS 510A PO Box 5000 Upton NY 11973-5000
> tel office : 631-344-7894; fax 631-344-4206; home 631-345-2690




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