First description of the interface (#8)

* First description of the interface
* added method that returns the preferred coordinate syste,
* fixed doc on interface

---------

Co-authored-by: Mikhail Mikhasenko <mikhail.mikhasenko@cern.ch>

docs/src/10-interface.md

@@ -0,0 +1,67 @@
+# [Interface](@id interface)
+
+## Implementation
+
+This section explains how the object can become a `LorentzVector`. A type `MyLorentzVector` will comply to the `LorentzVector` interface if one of the following et of methods is implemented.
+
+### Option 1: position with cartesian coordinates
+
+| Required Methods                                             | Brief Description                               |
+|--------------------------------------------------------------|-------------------------------------------------|
+| `LorentzVectorBase.islorentzvector(::Type{MyLorentzVector})` | Declare that your type implements the interface |
+| `LorentzVectorBase.coordinatesystem(::Type{MyLorentzVector}) = LorentzVectorBase.XYZE`  | Declare the preferred coordinated system |
+| `LorentzVectorBase.x(::Tupe{MyLorentzVector})`               | x cartesian coordinate                          |
+| `LorentzVectorBase.y(::Tupe{MyLorentzVector})`               | y cartesian coordinate                          |
+| `LorentzVectorBase.z(::Tupe{MyLorentzVector})`               | z cartesian coordinate                          |
+| `LorentzVectorBase.t(::Tupe{MyLorentzVector})`               | t cartesian coordinate                          |
+|                                                              |                                                 |
+
+
+### Option 2: four-momentum with catesian coordinates
+
+| Required Methods                                             | Brief Description                               |
+|--------------------------------------------------------------|-------------------------------------------------|
+| `LorentzVectorBase.islorentzvector(::Type{MyLorentzVector})` | Declare that your type implements the interface |
+| `LorentzVectorBase.coordinatesystem(::Type{MyLorentzVector}) = LorentzVectorBase.XYZE`  | Declare the preferred coordinated system |
+| `LorentzVectorBase.px(::Tupe{MyLorentzVector})`              | x cartesian coordinate                          |
+| `LorentzVectorBase.py(::Tupe{MyLorentzVector})`              | y cartesian coordinate                          |
+| `LorentzVectorBase.pz(::Tupe{MyLorentzVector})`              | z cartesian coordinate                          |
+| `LorentzVectorBase.pt(::Tupe{MyLorentzVector})`              | t cartesian coordinate                          |
+|                                                              |                                                 |
+
+### Option 3 four-momentum with cylindrical coordinates
+
+| Required Methods                                             | Brief Description                               |
+|--------------------------------------------------------------|-------------------------------------------------|
+| `LorentzVectorBase.islorentzvector(::Type{MyLorentzVector})` | Declare that your type implements the interface |
+| `LorentzVectorBase.coordinatesystem(::Type{MyLorentzVector})`| Declare the preferred coordinated system. Must return PtEtaPhiM, PtEtaPhiE, PtYPhiM, or PtYPhiE (from LorentzVectorBase).|
+| `LorentzVectorBase.pt(::Tupe{MyLorentzVector})`              | x cartesian coordinate                          |
+| `LorentzVectorBase.phi(::Tupe{MyLorentzVector})`             | z cartesian coordinate                          |
+
+<br>
+and *one of*
+
+|   |   |
+|---|---|
+| `LorentzVectorBase.eta(::Tupe{MyLorentzVector})`             | y cartesian coordinate                          |
+| `LorentzVectorBase.rapidity(::Tupe{MyLorentzVector})`        | y cartesian coordinate                          |
+
+<br>
+and *one of*
+
+| | |
+|-|-|
+| `LorentzVectorBase.energy(::Tupe{MyLorentzVector})`          | energy          |
+| `LorentzVectorBase.mass(::Tupe{MyLorentzVector})`            | invariant mass  |
+
+The methods that returns the coordinates of the prefered system (returned by `coordinatesystem()`) must be implemented.
+
+## Optional methods
+
+| | |
+|-|-|
+| `LorentzVectorBase.mass2(::MyType{MyLorentzVector})`              | mass to the square |
+| `LorentzVectorBase.spatial_magnitude2(::MyType{MyLorentzVector})` | mass to the square |
+| Any of the above method i.e, a method of option Y when methods of option X are provided ||
+
+=======

docs/src/index.md

@@ -6,4 +6,3 @@ CurrentModule = LorentzVectorBase
 
 Documentation for [LorentzVectorBase](https://github.com/JuliaHEP/LorentzVectorBase.jl).
 
-