def sample(forest, B, v=None):
""" Sample from parse forest. """
if v is None:
v = forest.root
edges = forest.incoming[v]
if not edges:
# base case (leaf), nothing to sample
return v
# sample incoming edge, p(e|head) \propto edge.weight * (\prod_{b in e.body} beta[b])
Z = LogVal.Zero()
cs = []
for e in edges:
p = e.weight
for y in e.body:
p *= B[y]
Z += p
cs.append(Z.to_real())
# sample one of the incoming edges
i = np.array(cs).searchsorted(uniform(0, cs[-1]))
e = edges[i]
return Tree(v, [sample(forest, B, y) for y in e.body])
def _test_sample_tree(example, grammar, N):
# gold = {(X,I,K) for (X,I,K) in example.gold_items if (I,K) in example.nodes}
print()
_forest = parse_forest(example, grammar)
# apply temperature to grammar rules
forest = Hypergraph()
forest.root = _forest.root
for e in _forest.edges:
c = LogVal.Zero()
c.logeq(e.weight)
forest.edge(c, e.head, *e.body)
# run inside-outside
B, A = sum_product(forest)
Z = B[forest.root]
# compute marginals and recall from samples
# sample_recall = 0.0
m = defaultdict(float)
for _ in iterview(range(N)):
t = sample(forest, B)
for s in t.subtrees():
x = s.label()
m[x] += 1.0 / N
# xx = rename(grammar, x)
# sample_recall += (xx in gold) * 1.0 / N
# convert node names and marginalize-out time index
IO = defaultdict(float)
for x in forest.incoming:
IO[x] += (B[x] * A[x] / Z).to_real()
# check marginals
threshold = 1e-4
for x in IO:
(I, K, X, T) = x
if K - I > 1:
a = IO[x]
b = m[x]
if a > threshold or b > threshold:
print('[%s %s %8s, %s] %7.3f %7.3f' \
% (I, K, X, T, a, b))
assert abs(a - b) < 0.05
def One(cls):
return cls(LogVal.One(), LogVal.Zero())
def Zero(cls):
return cls(LogVal.Zero(), LogVal.Zero())
def One():
return Semiring1(LogVal.One(), LogVal.Zero())
def One():
return Semiring2(LogVal.One(), LogVal.Zero(), LogValVector(),
LogValVector())