Remove process from diagram definition

src/FeynmanDiagramGenerator.jl

@@ -3,8 +3,12 @@ module FeynmanDiagramGenerator
 using QEDbase
 using QEDprocesses
 
+include("QEDprocesses_patch.jl")
+
 import Base.==
 
+export GenericQEDProcess, isphysical
+
 export AbstractTreeLevelFeynmanDiagram, FeynmanVertex, FeynmanDiagram
 export external_particles, virtual_particles, process, vertices
 
@@ -22,6 +26,8 @@ include("trees/print.jl")
 
 include("qft/qft.jl")
 
+include("generic_process_def.jl")
+
 include("diagrams/interface.jl")
 include("diagrams/vertex.jl")
 include("diagrams/diagrams.jl")

src/QEDprocesses_patch.jl

@@ -0,0 +1,7 @@
+# patch QEDprocesses
+# see issue https://github.com/QEDjl-project/QEDprocesses.jl/issues/77
+@inline function QEDprocesses.number_particles(
+    proc_def::AbstractProcessDefinition, dir::DIR, ::PT
+) where {DIR<:ParticleDirection,PT<:AbstractParticleType}
+    return count(x -> x isa PT, particles(proc_def, dir))
+end

src/diagrams/diagrams.jl

@@ -43,10 +43,8 @@ end
 # Feynman Diagram, tree-level, QED
 #
 
-struct FeynmanDiagram{PROC,N,E,U,T,M} <: AbstractTreeLevelFeynmanDiagram where {P<:AbstractProcessDefinition,N,E,U,T,M}
-    # E, U, T, and M can be inferred from the PROC, but not necessarily in 0 runtime
-    proc::PROC
-
+struct FeynmanDiagram{N,E,U,T,M} <: AbstractTreeLevelFeynmanDiagram where {N,E,U,T,M}
+    # TODO: flatten into one list
     diagram_structure::NTuple{N,Vector{Int}}
 
     electron_permutation::NTuple{E,Int}
@@ -54,7 +52,6 @@ struct FeynmanDiagram{PROC,N,E,U,T,M} <: AbstractTreeLevelFeynmanDiagram where {
     tauon_permutation::NTuple{T,Int}
 
     function FeynmanDiagram(
-        proc::PROC,
         structure::Vector{Vector{Int}},
         elec_perm::Vector{Int},
         muon_perm::Vector{Int},
@@ -63,18 +60,16 @@ struct FeynmanDiagram{PROC,N,E,U,T,M} <: AbstractTreeLevelFeynmanDiagram where {
         ::Val{U},
         ::Val{T},
         ::Val{M}
-    ) where {PROC<:AbstractProcessDefinition,E,U,T,M}
+    ) where {E,U,T,M}
         @assert E == length(elec_perm)
         @assert U == length(muon_perm)
         @assert T == length(tauon_perm)
         N = E + U + T
 
-        return new{PROC,N,E,U,T,M}(proc, NTuple{N,Vector{Int}}(structure), NTuple{E,Int}(elec_perm), NTuple{U,Int}(muon_perm), NTuple{T,Int}(tauon_perm))
+        return new{N,E,U,T,M}(NTuple{N,Vector{Int}}(structure), NTuple{E,Int}(elec_perm), NTuple{U,Int}(muon_perm), NTuple{T,Int}(tauon_perm))
     end
 end
 
-process(diagram::FeynmanDiagram) = d.proc
-
 function virtual_particles(diagram::FeynmanDiagram)
 
     return NTuple{N,Tuple{QEDbase.AbstractParticleType,BitArray}}()
@@ -159,8 +154,7 @@ function _external_photon_multiplicity(fermion_structure::Vector{Vector{Int}}, n
     return res
 end
 
-mutable struct FeynmanDiagramIterator{PROC<:AbstractProcessDefinition,E,U,T,M}
-    process::PROC
+mutable struct FeynmanDiagramIterator{E,U,T,M}
     e::Val{E}  # number of electron lines  (indices 1      - e)
     e_perms::Vector{Vector{Int}} # list of all the possible permutations of the electrons
     e_index::Int
@@ -175,14 +169,14 @@ mutable struct FeynmanDiagramIterator{PROC<:AbstractProcessDefinition,E,U,T,M}
     photon_structure::Vector{Vector{Int}} # current structure that's being permuted
 end
 
-function Base.length(it::FeynmanDiagramIterator{<:AbstractProcessDefinition,E,U,T,M}) where {E,U,T,M}
+function Base.length(it::FeynmanDiagramIterator{E,U,T,M}) where {E,U,T,M}
     N = E + U + T
     return factorial(M + 3 * N - 3, 2 * N - 1) * factorial(E) * factorial(U) * factorial(T)
 end
 
 function Base.iterate(iter::FeynmanDiagramIterator)
     return (
-        FeynmanDiagram(iter.process, iter.photon_structure, iter.e_perms[iter.e_index], iter.u_perms[iter.u_index], iter.t_perms[iter.t_index], iter.e, iter.u, iter.t, iter.m),
+        FeynmanDiagram(iter.photon_structure, iter.e_perms[iter.e_index], iter.u_perms[iter.u_index], iter.t_perms[iter.t_index], iter.e, iter.u, iter.t, iter.m),
         nothing
     )
 end
@@ -210,21 +204,35 @@ function Base.iterate(iter::FeynmanDiagramIterator, ::Nothing)
     end
 
     return (
-        FeynmanDiagram(iter.process, iter.photon_structure, iter.e_perms[iter.e_index], iter.u_perms[iter.u_index], iter.t_perms[iter.t_index], iter.e, iter.u, iter.t, iter.m),
+        FeynmanDiagram(iter.photon_structure, iter.e_perms[iter.e_index], iter.u_perms[iter.u_index], iter.t_perms[iter.t_index], iter.e, iter.u, iter.t, iter.m),
         nothing
     )
 end
 
-function feynman_diagrams(proc::PROC, e::Int, u::Int, t::Int, m::Int) where {PROC<:AbstractProcessDefinition}
-    if (e + u + t) * 2 + m < 4
-        throw(InvalidInputError("At least 4 particles must participate in a scattering process for a physical result!"))
+function feynman_diagrams(proc::PROC) where {PROC<:GenericQEDProcess}
+    return feynman_diagrams(incoming_particles(proc), outgoing_particles(proc))
 end
 
+function feynman_diagrams(in_particles::Tuple, out_particles::Tuple)
+    _assert_particle_type_tuple(in_particles)
+    _assert_particle_type_tuple(out_particles)
+
+    count(x -> x isa Electron, in_particles) + count(x -> x isa Positron, out_particles) ==
+    count(x -> x isa Positron, in_particles) + count(x -> x isa Electron, out_particles) ||
+        throw(InvalidInputError("the given particles do not make a physical process"))
+
+    # get the fermion line counts and external photon count
+    e = count(x -> x isa Electron, in_particles) + count(x -> x isa Positron, out_particles)
+    m = count(x -> x isa Photon, in_particles) + count(x -> x isa Photon, out_particles)
+    # TODO: do this the same way as for e when muons and tauons are a part of QED.jl
+    u = 0
+    t = 0
+
     f_iter = _feynman_structures(e + u + t, m)
     e_perms = collect(permutations(Int[1:e;]))
     u_perms = collect(permutations(Int[e+1:e+u;]))
     t_perms = collect(permutations(Int[e+u+1:e+u+t;]))
     first_photon_structure, _ = iterate(f_iter)
 
-    return FeynmanDiagramIterator(proc, Val(e), e_perms, 1, Val(u), u_perms, 1, Val(t), t_perms, 1, Val(m), f_iter, first_photon_structure)
+    return FeynmanDiagramIterator(Val(e), e_perms, 1, Val(u), u_perms, 1, Val(t), t_perms, 1, Val(m), f_iter, first_photon_structure)
 end

src/generic_process_def.jl

@@ -0,0 +1,34 @@
+using QEDprocesses
+
+_assert_particle_type_tuple(::Tuple{}) = nothing
+_assert_particle_type_tuple(t::Tuple{AbstractParticleType,Vararg}) = _assert_particle_type_tuple(t[2:end])
+_assert_particle_type_tuple(t::Any) = throw(InvalidInputError("invalid input, provide a tuple of AbstractParticleTypes to construct a GenericQEDProcess"))
+
+struct GenericQEDProcess{INT,OUTT} <: AbstractProcessDefinition where {INT<:Tuple,OUTT<:Tuple}
+    incoming_particles::INT
+    outgoing_particles::OUTT
+
+    function GenericQEDProcess(in_particles::INT, out_particles::OUTT) where {INT<:Tuple,OUTT<:Tuple}
+        _assert_particle_type_tuple(in_particles)
+        _assert_particle_type_tuple(out_particles)
+
+        #feynman_diagrams((), ())
+
+        return new{INT,OUTT}(in_particles, out_particles)
+    end
+end
+
+QEDprocesses.incoming_particles(proc::GenericQEDProcess) = proc.incoming_particles
+QEDprocesses.outgoing_particles(proc::GenericQEDProcess) = proc.outgoing_particles
+
+function isphysical(proc::GenericQEDProcess)
+    return (number_particles(proc, Incoming(), Electron()) + number_particles(proc, Outgoing(), Positron()) ==
+            number_particles(proc, Incoming(), Positron()) + number_particles(proc, Outgoing(), Electron())) &&
+           number_particles(proc, Incoming()) + number_particles(proc, Outgoing()) >= 2
+end
+
+function matrix_element(proc::GenericQEDProcess, psp::PhaseSpacePoint)
+
+
+    return nothing
+end