def subgraph(self, v):
"""
Creates a subgraph by performing DFS in the current digraph
for node v and taking any nodes and edges traversed to the
subgraph.
returns Digraph
"""
from pygraph.algorithms.traversal import NodeVisitor, dfs
class Visitor(NodeVisitor):
def __init__(self, result):
self.result = result
def visit_node(self, dg, v):
self.result.add_node(v)
def visit_edge(self, dg, v, w):
self.result.add_edge(v, w)
dg = Digraph()
visitor = Visitor(dg)
dfs(self, v, visitor)
return dg
def subgraph(self, v):
"""
Creates a subgraph by performing DFS in the current digraph
for node v and taking any nodes and edges traversed to the
subgraph.
returns Digraph
"""
from pygraph.algorithms.traversal import NodeVisitor, dfs
class Visitor(NodeVisitor):
def __init__(self, result):
self.result = result
def visit_node(self, dg, v):
self.result.add_node(v)
def visit_edge(self, dg, v, w):
self.result.add_edge(v, w)
dg = Digraph()
visitor = Visitor(dg)
dfs(self, v, visitor)
return dg
def acyclic_closure(digraph):
"""
@digraph: Digraph
Generates reachability matrix for an acyclic digraph.
Reachability matrix allows for constant time querying
of whether node i can reach node j in a digraph.
"""
matrix = ByteNodeMatrix()
for i in digraph.nodes_set():
for j in digraph.nodes_set():
reaches = (i == j) or traversal.dfs(digraph, i, None, lambda v: v != j)
if reaches:
matrix.set(i, j, 1)
else:
matrix.set(i, j, 0)
return matrix
def acyclic_closure(digraph):
"""
@digraph: Digraph
Generates reachability matrix for an acyclic digraph.
Reachability matrix allows for constant time querying
of whether node i can reach node j in a digraph.
"""
matrix = ByteNodeMatrix()
for i in digraph.nodes_set():
for j in digraph.nodes_set():
reaches = (i == j) or traversal.dfs(digraph, i, None,
lambda v: v != j)
if reaches:
matrix.set(i, j, 1)
else:
matrix.set(i, j, 0)
return matrix
