def find_model_for(self, sentence, number_of_flips,
probability_of_random_walk):
model = Model()
cnf_sentence = CNFTransformer().transform(sentence)
clauses = CNFClauseGatherer().collect(cnf_sentence)
symbols = SymbolsCollector().collect_symbols(sentence)
# model <- a random assignment of true/false to the symbols in clauses
for symbol in symbols:
model = model.extend(symbol, randbool())
# for i = 1 to max_flips do
for i in range(number_of_flips):
# if model satisfies clauses then return model
if self._all_clauses_satisfied(clauses, model):
return model
# clause <- a randomly selected clause from clauses that is false in model
symbols_list = list(
self._get_symbols_of_randomly_selected_false_clause(
clauses, model))
# with probability p flip the value in model of a randomly selected symbol from clause
if random.random() >= probability_of_random_walk:
symbol = select_randomly_from_list(symbols_list)
# else flip whichever symbol in clause maximizes the number of satisfied clauses
else:
symbol = self._get_symbol_whose_flip_maximises_satisfied_clauses(
clauses, model, symbols_list)
model.flip(symbol)
return None
def find_model_for(self, sentence, number_of_flips, probability_of_random_walk):
model = Model()
cnf_sentence = CNFTransformer().transform(sentence)
clauses = CNFClauseGatherer().collect(cnf_sentence)
symbols = SymbolsCollector().collect_symbols(sentence)
# model <- a random assignment of true/false to the symbols in clauses
for symbol in symbols:
model = model.extend(symbol, randbool())
# for i = 1 to max_flips do
for i in range(number_of_flips):
# if model satisfies clauses then return model
if self._all_clauses_satisfied(clauses, model):
return model
# clause <- a randomly selected clause from clauses that is false in model
symbols_list = list(self._get_symbols_of_randomly_selected_false_clause(clauses, model))
# with probability p flip the value in model of a randomly selected symbol from clause
if random.random() >= probability_of_random_walk:
symbol = select_randomly_from_list(symbols_list)
# else flip whichever symbol in clause maximizes the number of satisfied clauses
else:
symbol = self._get_symbol_whose_flip_maximises_satisfied_clauses(clauses, model, symbols_list)
model.flip(symbol)
return None
