Proposal for PhaseSpacePoint improvement (#63)

Proposal for a rework of the PhaseSpacePoint, according to Issue #58

I did a lot of type magic with recursive variadic templates to find out
type information and get functions perfectly type stable. Constructing
phase space points is now always type stable and takes a maximum of
~11ns for me when constructing from momenta.

Some of the tests are failing for now because some of the interfaces
currently don't expect tuples from the PSP implementation. It might make
sense to fix this in #59

---------

Co-authored-by: Uwe Hernandez Acosta <u.hernandez@hzdr.de>
Co-authored-by: Uwe Hernandez Acosta <szabo137@users.noreply.github.com>
Co-authored-by: AntonReinhard <anton.reinhard@protonmail.com>

src/QEDprocesses.jl

@@ -35,8 +35,7 @@ export AbstractCoordinateSystem, SphericalCoordinateSystem
 export AbstractFrameOfReference, CenterOfMomentumFrame, ElectronRestFrame
 export AbstractPhasespaceDefinition, PhasespaceDefinition
 export ParticleStateful, PhaseSpacePoint
-export spin, polarization, particle_direction, particle_species, momentum, getindex
-export generate_phase_space
+export spin, polarization, particle_direction, particle_species, momentum, momenta, getindex
 
 # specific compute models
 export PerturbativeQED

src/cross_section/diff_cross_section.jl

@@ -6,7 +6,7 @@
 ########################
 
 function _incident_flux(psp::PhaseSpacePoint)
-    return _incident_flux(psp.proc, psp.model, momentum.(psp.in_particles))
+    return _incident_flux(psp.proc, psp.model, momenta(psp, Incoming()))
 end
 
 """

src/cross_section/internal.jl

@@ -10,9 +10,7 @@ function _unsafe_differential_probability(
     in_phase_space::AbstractVector{T},
     out_phase_space::AbstractVector{T},
 ) where {T<:QEDbase.AbstractFourMomentum}
-    psp = generate_phase_space(
-        proc, model, phase_space_def, in_phase_space, out_phase_space
-    )
+    psp = PhaseSpacePoint(proc, model, phase_space_def, in_phase_space, out_phase_space)
     return unsafe_differential_probability(psp)
 end
 
@@ -45,9 +43,7 @@ function _differential_probability(
     in_phase_space::AbstractVector{T},
     out_phase_space::AbstractVector{T},
 ) where {T<:QEDbase.AbstractFourMomentum}
-    psp = generate_phase_space(
-        proc, model, phase_space_def, in_phase_space, out_phase_space
-    )
+    psp = PhaseSpacePoint(proc, model, phase_space_def, in_phase_space, out_phase_space)
     return differential_probability(psp)
 end
 
@@ -79,9 +75,7 @@ function _unsafe_differential_cross_section(
     in_phase_space::AbstractVector{T},
     out_phase_space::AbstractVector{T},
 ) where {T<:QEDbase.AbstractFourMomentum}
-    psp = generate_phase_space(
-        proc, model, phase_space_def, in_phase_space, out_phase_space
-    )
+    psp = PhaseSpacePoint(proc, model, phase_space_def, in_phase_space, out_phase_space)
     return unsafe_differential_cross_section(psp)
 end
 
@@ -114,9 +108,7 @@ function _differential_cross_section(
     in_phase_space::AbstractVector{T},
     out_phase_space::AbstractVector{T},
 ) where {T<:QEDbase.AbstractFourMomentum}
-    psp = generate_phase_space(
-        proc, model, phase_space_def, in_phase_space, out_phase_space
-    )
+    psp = PhaseSpacePoint(proc, model, phase_space_def, in_phase_space, out_phase_space)
     return differential_cross_section(psp)
 end
 

src/interfaces/process_interface.jl

@@ -140,7 +140,6 @@ function _phase_space_factor end
 #######################
 
 """
-
     number_incoming_particles(proc_def::AbstractProcessDefinition)
 
 Return the number of incoming particles of a given process. 
@@ -150,7 +149,6 @@ Return the number of incoming particles of a given process.
 end
 
 """
-
     number_outgoing_particles(proc_def::AbstractProcessDefinition)
 
 Return the number of outgoing particles of a given process.