124 lines
5.0 KiB
Python
124 lines
5.0 KiB
Python
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# -*- coding: utf-8 -*-
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"""
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Tests for IBM Model 4 training methods
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"""
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import unittest
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from collections import defaultdict
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from nltk.translate import AlignedSent
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from nltk.translate import IBMModel
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from nltk.translate import IBMModel4
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from nltk.translate.ibm_model import AlignmentInfo
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class TestIBMModel4(unittest.TestCase):
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def test_set_uniform_distortion_probabilities_of_max_displacements(self):
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# arrange
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src_classes = {'schinken': 0, 'eier': 0, 'spam': 1}
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trg_classes = {'ham': 0, 'eggs': 1, 'spam': 2}
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corpus = [
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AlignedSent(['ham', 'eggs'], ['schinken', 'schinken', 'eier']),
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AlignedSent(['spam', 'spam', 'spam', 'spam'], ['spam', 'spam']),
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]
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model4 = IBMModel4(corpus, 0, src_classes, trg_classes)
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# act
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model4.set_uniform_probabilities(corpus)
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# assert
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# number of displacement values =
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# 2 *(number of words in longest target sentence - 1)
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expected_prob = 1.0 / (2 * (4 - 1))
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# examine the boundary values for (displacement, src_class, trg_class)
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self.assertEqual(model4.head_distortion_table[3][0][0], expected_prob)
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self.assertEqual(model4.head_distortion_table[-3][1][2], expected_prob)
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self.assertEqual(model4.non_head_distortion_table[3][0], expected_prob)
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self.assertEqual(model4.non_head_distortion_table[-3][2], expected_prob)
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def test_set_uniform_distortion_probabilities_of_non_domain_values(self):
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# arrange
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src_classes = {'schinken': 0, 'eier': 0, 'spam': 1}
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trg_classes = {'ham': 0, 'eggs': 1, 'spam': 2}
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corpus = [
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AlignedSent(['ham', 'eggs'], ['schinken', 'schinken', 'eier']),
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AlignedSent(['spam', 'spam', 'spam', 'spam'], ['spam', 'spam']),
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]
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model4 = IBMModel4(corpus, 0, src_classes, trg_classes)
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# act
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model4.set_uniform_probabilities(corpus)
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# assert
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# examine displacement values that are not in the training data domain
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self.assertEqual(model4.head_distortion_table[4][0][0], IBMModel.MIN_PROB)
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self.assertEqual(model4.head_distortion_table[100][1][2], IBMModel.MIN_PROB)
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self.assertEqual(model4.non_head_distortion_table[4][0], IBMModel.MIN_PROB)
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self.assertEqual(model4.non_head_distortion_table[100][2], IBMModel.MIN_PROB)
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def test_prob_t_a_given_s(self):
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# arrange
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src_sentence = ["ich", 'esse', 'ja', 'gern', 'räucherschinken']
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trg_sentence = ['i', 'love', 'to', 'eat', 'smoked', 'ham']
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src_classes = {'räucherschinken': 0, 'ja': 1, 'ich': 2, 'esse': 3, 'gern': 4}
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trg_classes = {'ham': 0, 'smoked': 1, 'i': 3, 'love': 4, 'to': 2, 'eat': 4}
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corpus = [AlignedSent(trg_sentence, src_sentence)]
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alignment_info = AlignmentInfo(
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(0, 1, 4, 0, 2, 5, 5),
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[None] + src_sentence,
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['UNUSED'] + trg_sentence,
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[[3], [1], [4], [], [2], [5, 6]],
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)
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head_distortion_table = defaultdict(
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lambda: defaultdict(lambda: defaultdict(float))
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)
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head_distortion_table[1][None][3] = 0.97 # None, i
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head_distortion_table[3][2][4] = 0.97 # ich, eat
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head_distortion_table[-2][3][4] = 0.97 # esse, love
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head_distortion_table[3][4][1] = 0.97 # gern, smoked
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non_head_distortion_table = defaultdict(lambda: defaultdict(float))
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non_head_distortion_table[1][0] = 0.96 # ham
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translation_table = defaultdict(lambda: defaultdict(float))
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translation_table['i']['ich'] = 0.98
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translation_table['love']['gern'] = 0.98
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translation_table['to'][None] = 0.98
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translation_table['eat']['esse'] = 0.98
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translation_table['smoked']['räucherschinken'] = 0.98
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translation_table['ham']['räucherschinken'] = 0.98
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fertility_table = defaultdict(lambda: defaultdict(float))
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fertility_table[1]['ich'] = 0.99
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fertility_table[1]['esse'] = 0.99
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fertility_table[0]['ja'] = 0.99
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fertility_table[1]['gern'] = 0.99
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fertility_table[2]['räucherschinken'] = 0.999
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fertility_table[1][None] = 0.99
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probabilities = {
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'p1': 0.167,
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'translation_table': translation_table,
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'head_distortion_table': head_distortion_table,
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'non_head_distortion_table': non_head_distortion_table,
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'fertility_table': fertility_table,
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'alignment_table': None,
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}
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model4 = IBMModel4(corpus, 0, src_classes, trg_classes, probabilities)
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# act
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probability = model4.prob_t_a_given_s(alignment_info)
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# assert
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null_generation = 5 * pow(0.167, 1) * pow(0.833, 4)
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fertility = 1 * 0.99 * 1 * 0.99 * 1 * 0.99 * 1 * 0.99 * 2 * 0.999
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lexical_translation = 0.98 * 0.98 * 0.98 * 0.98 * 0.98 * 0.98
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distortion = 0.97 * 0.97 * 1 * 0.97 * 0.97 * 0.96
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expected_probability = (
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null_generation * fertility * lexical_translation * distortion
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)
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self.assertEqual(round(probability, 4), round(expected_probability, 4))
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