def add_random_edge(dag: DAG,
node_order: List[str],
max_in_degree: int = 4) -> None:
"""Add a random edge to the graph, that respects the given node_order, and
also doesn't add a link if the sampled node has maximal in_degree already.
It may not add any edge.
"""
n1, n2 = random.sample(node_order, 2)
if node_order.index(n1) < node_order.index(n2) and dag.in_degree(
n2) < max_in_degree:
dag.add_edge(n1, n2)
elif node_order.index(n2) < node_order.index(n1) and dag.in_degree(
n1) < max_in_degree:
dag.add_edge(n2, n1)
def random_dag(number_of_nodes: int = 5,
edge_density: float = 0.4,
max_in_degree: int = 4) -> DAG:
"""Create a connected, random directed acyclic graph (DAG), with the given number of nodes,
the given edge density, and with no node exceeding having too high in degree"""
node_names = [f"X{i}" for i in range(number_of_nodes)]
dag = DAG()
# First make sure the dag is connected
visited = list()
unvisited = list(node_names)
node = random.choice(unvisited)
unvisited.remove(node)
visited.append(node)
dag.add_node(node)
while unvisited:
node = random.choice(unvisited)
neighbor = random.choice(visited)
if node_names.index(node) < node_names.index(
neighbor) and dag.in_degree(neighbor) < max_in_degree:
dag.add_edge(node, neighbor)
elif node_names.index(neighbor) < node_names.index(node):
dag.add_edge(neighbor, node)
else:
continue
unvisited.remove(node)
visited.append(node)
# Then add edges until desired density is reached
maximum_number_of_edges = number_of_nodes * (number_of_nodes - 1) / 2
while dag.number_of_edges() < int(edge_density * maximum_number_of_edges):
add_random_edge(dag, node_names)
return dag
