End of Day; Add topology generation and iterators

src/diagrams/diagrams.jl

@@ -0,0 +1,37 @@
+using Combinatorics
+
+struct FeynmanDiagramDefinition
+    n::Int
+end
+
+struct FeynmanDiagramTopology
+    # largest subtree
+    subtree1::AbstractTree
+    # second largest subtree
+    subtree2::AbstractTree
+    # third largest subtree
+    subtree3::AbstractTree
+end
+
+struct TopologyPartition
+    leaves1::Int
+    leaves2::Int
+    leaves3::Int
+end
+
+function is_valid(partition::TopologyPartition)
+    if partition.leaves2 > partition.leaves1 || partition.leaves3 > partition.leaves2
+        return false
+    end
+    if partition.leaves1 > partition.leaves2 + partition.leaves3
+        return false
+    end
+    if partition.leaves1 <= 0 || partition.leaves2 <= 0 || partition.leaves3 <= 0
+        return false
+    end
+    return true
+end
+
+function leaves(partition::TopologyPartition)
+    return partition.leaves1 + partition.leaves2 + partition.leaves3
+end

src/diagrams/iterator.jl

@@ -0,0 +1,92 @@
+
+"""
+    iterates inside one partition
+"""
+mutable struct FeynmanPartitionIterator
+    topology::TopologyPartition
+    forest1_iterator::Union{ForestIterator,Missing}
+    forest2_iterator::Union{ForestIterator,Missing}
+    forest3_iterator::Union{ForestIterator,Missing}
+end
+
+mutable struct FeynmanDiagramTopologyIterator
+    leaves::Int
+    partitions_state::Vector{Int64}
+    partition::FeynmanPartitionIterator
+end
+
+function FeynmanPartitionIterator(topology::TopologyPartition)
+    return FeynmanPartitionIterator(topology, ForestIterator(topology.leaves1), ForestIterator(topology.leaves2), ForestIterator(topology.leaves3))
+end
+
+function FeynmanDiagramTopologyIterator(def::FeynmanDiagramDefinition)
+    @assert def.n >= 4 "A Feynman diagram must have at least 4 legs"
+    (p, _) = iterate(partitions(def.n))
+    while length(p) != 3 || !is_valid(TopologyPartition(p[1], p[2], p[3]))
+        (p, _) = iterate(partitions(def.n), p)
+    end
+    return FeynmanDiagramTopologyIterator(def.n, p, FeynmanPartitionIterator(TopologyPartition(p[1], p[2], p[3])))
+end
+
+function FeynmanDiagramTopology(iterator::FeynmanPartitionIterator)
+    return FeynmanDiagramTopology(tree(iterator.forest1_iterator), tree(iterator.forest2_iterator), tree(iterator.forest3_iterator))
+end
+
+function FeynmanDiagramTopology(iterator::FeynmanDiagramTopologyIterator)
+    return FeynmanDiagramTopology(iterator.partition)
+end
+
+function _iterate(iterator::FeynmanPartitionIterator)
+    # todo: need symmetry breaking here
+    if !is_end(iterator.forest3_iterator)
+        _iterate(iterator.forest3_iterator)
+    elseif !is_end(iterator.forest2_iterator)
+        iterator.forest3_iterator = ForestIterator(iterator.topology.leaves3)
+        _iterate(iterator.forest2_iterator)
+    else
+        iterator.forest3_iterator = ForestIterator(iterator.topology.leaves3)
+        iterator.forest2_iterator = ForestIterator(iterator.topology.leaves2)
+        _iterate(iterator.forest1_iterator)
+    end
+    return nothing
+end
+
+function _iterate(iterator::FeynmanDiagramTopologyIterator)
+    if !is_end(iterator.partition)
+        _iterate(iterator.partition)
+    else
+        while true
+            ret = iterate(partitions(iterator.leaves), iterator.partitions_state)
+
+            if (isnothing(ret))
+                return false
+            end
+
+            (p, _) = ret
+            iterator.partitions_state = p
+            if length(p) == 3 && is_valid(TopologyPartition(p[1], p[2], p[3]))
+                iterator.partition = FeynmanPartitionIterator(TopologyPartition(p[1], p[2], p[3]))
+                break
+            end
+        end
+    end
+    return true
+end
+
+function is_end(iterator::FeynmanPartitionIterator)
+    return is_end(iterator.forest1_iterator) && is_end(iterator.forest2_iterator) && is_end(iterator.forest3_iterator)
+end
+
+function iterate(def::FeynmanDiagramDefinition)
+    state = FeynmanDiagramTopologyIterator(def)
+
+    return (FeynmanDiagramTopology(state), state)
+end
+
+function iterate(def::FeynmanDiagramDefinition, state::FeynmanDiagramTopologyIterator)
+    if !_iterate(state)
+        return nothing
+    end
+
+    return (FeynmanDiagramTopology(state), state)
+end