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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 variable's domain change.
"""
alias CPSolver.Propagator
alias CPSolver.Variable.Interface
alias CPSolver.DefaultDomain, as: Domain
@spec create([Propagator.t()]) :: Graph.t()
def create(propagators) when is_list(propagators) do
Enum.reduce(propagators, Graph.new(), fn p, graph_acc ->
add_propagator(graph_acc, p)
end)
end
def propagators_by_variable(constraint_graph, variable_id, reduce_fun)
when is_function(reduce_fun, 2) do
constraint_graph
|> Graph.edges(variable_vertex(variable_id))
|> Enum.reduce(Map.new(), fn edge, acc ->
{:propagator, p_id} = edge.v2
((p_data = reduce_fun.(p_id, edge.label)) && p_data && Map.put(acc, p_id, p_data)) ||
acc
end)
end
## Get a list of propagator ids that "listen" to the domain change of given variable.
def get_propagator_ids(
constraint_graph,
variable_id,
domain_change
) do
propagators_by_variable(constraint_graph, variable_id, fn p_id, propagator_variable_edge ->
domain_change in propagator_variable_edge.propagate_on &&
get_propagator_data(
propagator_variable_edge,
domain_change,
get_propagator(constraint_graph, p_id)
)
end)
end
defp get_propagator_data(_edge, domain_change, propagator) do
%{
domain_change: domain_change,
propagator: propagator
}
end
def has_variable?(graph, variable_id) do
Graph.has_vertex?(graph, variable_vertex(variable_id))
end
def add_variable(graph, variable) do
Graph.add_vertex(graph, variable_vertex(variable.id), [variable])
end
def add_propagator(graph, propagator) do
propagator_vertex = propagator_vertex(propagator.id)
propagator
|> Propagator.variables()
|> Enum.reduce(graph, fn var, graph_acc ->
interface_var = Interface.variable(var)
graph_acc
|> add_variable(interface_var)
|> Graph.add_vertex(propagator_vertex)
|> then(fn graph ->
(Interface.domain(interface_var) |> Domain.fixed?() && graph) ||
Graph.add_edge(graph, variable_vertex(interface_var.id), propagator_vertex,
label: %{
propagate_on: get_propagate_on(var),
variable_name: interface_var.name
}
)
end)
end)
|> Graph.label_vertex(propagator_vertex, propagator)
end
def get_propagator(%Graph{} = graph, {:propagator, _propagator_id} = vertex) do
get_label(graph, vertex)
end
def get_propagator(graph, propagator_id) do
get_propagator(graph, propagator_vertex(propagator_id))
end
def update_propagator(
%Graph{vertex_labels: labels, vertex_identifier: identifier} = graph,
propagator_id,
propagator
) do
vertex = propagator_vertex(propagator_id)
graph
|> Map.put(:vertex_labels, Map.put(labels, identifier.(vertex), [propagator]))
end
def variable_vertex(variable_id) do
{:variable, variable_id}
end
def propagator_vertex(propagator_id) do
{:propagator, propagator_id}
end
def variable_degree(%Graph{} = graph, variable_id) do
Graph.out_degree(graph, variable_vertex(variable_id))
end
def propagator_degree(%Graph{} = graph, propagator_id) do
Graph.in_degree(graph, propagator_vertex(propagator_id))
end
def remove_propagator(graph, propagator_id) do
remove_vertex(graph, propagator_vertex(propagator_id))
end
def remove_edge(graph, var_id, propagator_id) do
Graph.delete_edge(graph, variable_vertex(var_id), propagator_vertex(propagator_id))
end
def entailed_propagator?(graph, propagator) do
Enum.empty?(Graph.neighbors(graph, propagator_vertex(propagator.id)))
end
def get_variable(%Graph{} = graph, {:variable, _variable_id} = vertex) do
get_label(graph, vertex)
end
def get_variable(graph, variable_id) do
get_variable(graph, variable_vertex(variable_id))
end
## Remove variable
def remove_variable(graph, variable_id) do
remove_vertex(graph, variable_vertex(variable_id))
end
def disconnect_variable(graph, variable_id) do
Graph.delete_edges(graph, Graph.edges(graph, variable_vertex(variable_id)))
end
### This is called on creation of new space.
###
### Stop notifications from fixed variables and update propagators with variable domains.
### Returns updated graph and a list of propagators bound to variable domains
def update(graph, vars) do
{updated_var_graph, propagators} =
Enum.reduce(vars, {graph, MapSet.new()}, fn %{id: var_id} = v,
{graph_acc, propagators_acc} ->
{update_variable(graph_acc, var_id, v),
MapSet.union(
propagators_acc,
MapSet.new(
Map.keys(propagators_by_variable(graph, Interface.id(v), fn _p_id, edge -> edge end))
)
)}
end)
## Update domains
propagators
|> Enum.reduce({updated_var_graph, []}, fn p_id, {graph_acc, p_acc} ->
graph_acc
|> get_propagator(p_id)
|> Propagator.bind(updated_var_graph, :domain)
|> then(fn bound_p ->
{
update_propagator(graph_acc, p_id, bound_p),
[bound_p | p_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
defp get_label(%Graph{} = graph, vertex) do
case Graph.vertex_labels(graph, vertex) do
[] -> nil
[p] -> p
end
end
def update_variable(
%Graph{vertex_labels: labels, vertex_identifier: identifier} = graph,
var_id,
variable
) do
vertex = variable_vertex(var_id)
Map.put(graph, :vertex_labels, Map.put(labels, identifier.(vertex), [variable]))
end
end