Re: Proposal for new Physics Vector classes in ROOT

Hi Brett,

  it is not a stupid question.
When used in Geometry, it is sometimes preferable to distinguish between Position Vectors, points, and Displacement Vectors which represent displacements with their corresponding direction. They have different transformations, for example the Position Vectors can rotate and translate while the Displacement Vectors can only rotate. The translation has no effect on them. For example the Position Vector are used to represent space points, while unit Displacement Vectors rotation axis

More info I put in the doc attached to the package (see Points and Vector concept item).

  http://seal.web.cern.ch/seal/MathLibs/GenVector/0-1-0/html/index.html

We have this distinctions only for the 3D case, since the 4D case represent in the majority of the cases a kinematic (momentum) vector, thus a Displacement Vector in 4D.

  Best Regards,

  Lorenzo

On 7 Jun 2005, at 16:11, Brett Viren wrote:

> Hi Lorenzo,
>
> Lorenzo Moneta <Lorenzo.Moneta_at_cern.ch> writes:
>
>
>> XYZPoint p1;
>> Polar3DPoint p2;
>>
>> XYZVector v = p1 - p2;
>> double distance = v1.r();
>>
>
> Maybe it is a stupid question, but why do you differentiate between a
> point vector and a difference vector? A vector is a vector, no?
>
> Regards,
> -Brett.
>
>
>
Received on Tue Jun 07 2005 - 17:53:01 MEST