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Constraint Programming Solver
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lib/solver/core/propagator/constraint_graph.ex
defmodule CPSolver.Propagator.ConstraintGraph do
@moduledoc """
The constraint graph connects propagators and their variables.
The edge between a propagator and a variable represents a notification
the propagator receives upon varable's domain change.
"""
alias CPSolver.Propagator
alias CPSolver.Propagator.Variable
@spec create([Propagator.t()] | %{reference() => Propagator.t()}) :: Graph.t()
def create(propagators) when is_list(propagators) do
propagators
|> Enum.map(fn p -> {p.id, p} end)
|> Map.new()
|> create()
end
def create(propagators) when is_map(propagators) do
Enum.reduce(propagators, Graph.new(), fn {propagator_id,
%{mod: propagator_mod, args: args} = p},
acc ->
args
|> propagator_mod.variables()
|> Enum.reduce(acc, fn var, acc2 ->
Graph.add_vertex(acc2, {:propagator, propagator_id})
|> Graph.add_edge({:variable, var.id}, {:propagator, propagator_id},
label: get_propagate_on(var)
)
end)
|> Graph.label_vertex({:propagator, propagator_id}, p)
end)
end
## Get a list of propagator ids that "listen" to the domain change of given variable.
def get_propagators(
constraint_graph,
variable_id,
domain_change
) do
constraint_graph
|> Graph.edges({:variable, variable_id})
|> Enum.flat_map(fn edge ->
(domain_change in edge.label &&
Graph.vertex_labels(constraint_graph, edge.v2)) ||
[]
end)
end
def has_variable?(graph, variable_id) do
Graph.has_vertex?(graph, {:variable, variable_id})
end
def get_propagator(%Graph{} = graph, propagator_id) do
case Graph.vertex_labels(graph, {:propagator, propagator_id}) do
[] -> nil
[p] -> p
end
end
def remove_propagator(graph, propagator_id) do
remove_vertex(graph, {:propagator, propagator_id})
end
## Remove variable and all propagators that are isolated points as a result of variable removal
def remove_variable(graph, variable_id) do
var_vertex = {:variable, variable_id}
var_propagators = Graph.neighbors(graph, var_vertex)
graph
|> remove_vertex(var_vertex)
|> then(fn g ->
Enum.reduce(var_propagators, g, fn p_vertex, acc ->
# fix_propagator_variable(acc, p_vertex, variable_id)
(Graph.neighbors(acc, p_vertex) == [] && Graph.delete_vertex(acc, p_vertex)) ||
acc
end)
end)
end
def remove_fixed(graph, vars) do
Enum.reduce(vars, graph, fn v, acc ->
if Variable.fixed?(v) do
remove_variable(acc, v.id)
else
acc
end
end)
end
def remove_vertex(graph, vertex) do
Graph.delete_vertex(graph, vertex)
end
defp get_propagate_on(variable) do
Map.get(variable, :propagate_on, Propagator.to_domain_events(:fixed))
end
end