def test_cond_prob_normalization_2gram_no_addone(self):
model = BackOffNGram(2, self.sents, beta=0.5, addone=False)
alpha = 1.0 - (1.0 - 0.5) / 1.0
denom = model.denom(('el', ))
self.assertAlmostEqual(model.alpha(('el', )), alpha)
probs = {
('gato', 'el'): (1.0 - 0.5) / 1.0,
# back-off to the unigrams:
('el', 'el'): alpha * 1.0 / (12.0 * denom),
('come', 'el'): alpha * 2.0 / (12.0 * denom),
('pescado', 'el'): alpha * 1.0 / (12.0 * denom),
('.', 'el'): alpha * 2.0 / (12.0 * denom),
('</s>', 'el'): alpha * 2.0 / (12.0 * denom),
('la', 'el'): alpha * 1.0 / (12.0 * denom),
('gata', 'el'): alpha * 1.0 / (12.0 * denom),
('salmón', 'el'): alpha * 1.0 / (12.0 * denom),
}
for (token, prev), p in probs.items():
self.assertAlmostEqual(model.cond_prob(token, (prev, )),
p,
msg=(token, prev))
# the sum is one:
prob_sum = sum(probs.values())
self.assertAlmostEqual(prob_sum, 1.0)
def test_cond_prob_normalization_2gram_no_addone(self):
model = BackOffNGram(2, self.sents, beta=0.5, addone=False)
alpha = 1.0 - (1.0 - 0.5) / 1.0
denom = model.denom(('el',))
self.assertEqual(model.alpha(('el',)), alpha)
probs = {
('gato', 'el'): (1.0 - 0.5) / 1.0,
# back-off to the unigrams:
('el', 'el'): alpha * 1.0 / (12.0 * denom),
('come', 'el'): alpha * 2.0 / (12.0 * denom),
('pescado', 'el'): alpha * 1.0 / (12.0 * denom),
('.', 'el'): alpha * 2.0 / (12.0 * denom),
('</s>', 'el'): alpha * 2.0 / (12.0 * denom),
('la', 'el'): alpha * 1.0 / (12.0 * denom),
('gata', 'el'): alpha * 1.0 / (12.0 * denom),
('salmón', 'el'): alpha * 1.0 / (12.0 * denom),
}
for (token, prev), p in probs.items():
self.assertEqual(model.cond_prob(token, [prev]), p, (token, prev))
# the sum is one:
prob_sum = sum(probs.values())
self.assertTrue(abs(prob_sum - 1.0) < 1e-10, prob_sum)
def test_init_2gram(self):
model = BackOffNGram(2, self.sents, beta=0.5)
A = {
('<s>', ): {'el', 'la'},
('el', ): {'gato'},
('gato', ): {'come'},
('come', ): {'pescado', 'salmón'},
('pescado', ): {'.'},
('.', ): {'</s>'},
('la', ): {'gata'},
('gata', ): {'come'},
('salmón', ): {'.'},
}
for tokens, Aset in A.items():
self.assertEqual(model.A(tokens), Aset, tokens)
# missing probability mass
alpha = {
('<s>', ): 2 * 0.5 / 2,
('el', ): 1 * 0.5 / 1,
('gato', ): 1 * 0.5 / 1,
('come', ): 2 * 0.5 / 2,
('pescado', ): 1 * 0.5 / 1,
('.', ): 1 * 0.5 / 2,
('la', ): 1 * 0.5 / 1,
('gata', ): 1 * 0.5 / 1,
('salmón', ): 1 * 0.5 / 1,
}
for tokens, a in alpha.items():
self.assertAlmostEqual(model.alpha(tokens), a, msg=tokens)
# normalization factor
denom = {
('<s>', ):
1.0 - model.cond_prob('el') - model.cond_prob('la'),
('el', ):
1.0 - model.cond_prob('gato'),
('gato', ):
1.0 - model.cond_prob('come'),
('come', ):
1.0 - model.cond_prob('pescado') - model.cond_prob('salmón'),
('pescado', ):
1.0 - model.cond_prob('.'),
('.', ):
1.0 - model.cond_prob('</s>'),
('la', ):
1.0 - model.cond_prob('gata'),
('gata', ):
1.0 - model.cond_prob('come'),
('salmón', ):
1.0 - model.cond_prob('.'),
}
for tokens, d in denom.items():
self.assertAlmostEqual(model.denom(tokens), d, msg=tokens)
def test_init_2gram(self):
model = BackOffNGram(2, self.sents, beta=0.5)
A = {
('<s>',): {'el', 'la'},
('el',): {'gato'},
('gato',): {'come'},
('come',): {'pescado', 'salmón'},
('pescado',): {'.'},
('.',): {'</s>'},
('la',): {'gata'},
('gata',): {'come'},
('salmón',): {'.'},
}
for tokens, Aset in A.items():
self.assertEqual(model.A(tokens), Aset, tokens)
# missing probability mass
alpha = {
('<s>',): 2 * 0.5 / 2,
('el',): 1 * 0.5 / 1,
('gato',): 1 * 0.5 / 1,
('come',): 2 * 0.5 / 2,
('pescado',): 1 * 0.5 / 1,
('.',): 1 * 0.5 / 2,
('la',): 1 * 0.5 / 1,
('gata',): 1 * 0.5 / 1,
('salmón',): 1 * 0.5 / 1,
}
for tokens, a in alpha.items():
self.assertEqual(model.alpha(tokens), a, tokens)
# normalization factor
denom = {
('<s>',): 1.0 - model.cond_prob('el') - model.cond_prob('la'),
('el',): 1.0 - model.cond_prob('gato'),
('gato',): 1.0 - model.cond_prob('come'),
('come',): 1.0 - model.cond_prob('pescado') - model.cond_prob('salmón'),
('pescado',): 1.0 - model.cond_prob('.'),
('.',): 1.0 - model.cond_prob('</s>'),
('la',): 1.0 - model.cond_prob('gata'),
('gata',): 1.0 - model.cond_prob('come'),
('salmón',): 1.0 - model.cond_prob('.'),
}
for tokens, d in denom.items():
self.assertEqual(model.denom(tokens), d, tokens)