在Z3Py中,我如何检查给定约束的方程是否只有一个解?
如果有多个解决方案,我该如何枚举它们?
答案 0 :(得分:22)
您可以通过添加阻止Z3返回的模型的新约束来实现。
例如,假设在Z3返回的模型中,我们有x = 0
和y = 1
。然后,我们可以通过添加约束Or(x != 0, y != 1)
来阻止此模型。
以下脚本可以解决问题。
您可以在以下网址进行尝试:http://rise4fun.com/Z3Py/4blB
请注意,以下脚本有一些限制。输入公式不能包含未解释的函数,数组或未解释的排序。
from z3 import *
# Return the first "M" models of formula list of formulas F
def get_models(F, M):
result = []
s = Solver()
s.add(F)
while len(result) < M and s.check() == sat:
m = s.model()
result.append(m)
# Create a new constraint the blocks the current model
block = []
for d in m:
# d is a declaration
if d.arity() > 0:
raise Z3Exception("uninterpreted functions are not supported")
# create a constant from declaration
c = d()
if is_array(c) or c.sort().kind() == Z3_UNINTERPRETED_SORT:
raise Z3Exception("arrays and uninterpreted sorts are not supported")
block.append(c != m[d])
s.add(Or(block))
return result
# Return True if F has exactly one model.
def exactly_one_model(F):
return len(get_models(F, 2)) == 1
x, y = Ints('x y')
s = Solver()
F = [x >= 0, x <= 1, y >= 0, y <= 2, y == 2*x]
print get_models(F, 10)
print exactly_one_model(F)
print exactly_one_model([x >= 0, x <= 1, y >= 0, y <= 2, 2*y == x])
# Demonstrate unsupported features
try:
a = Array('a', IntSort(), IntSort())
b = Array('b', IntSort(), IntSort())
print get_models(a==b, 10)
except Z3Exception as ex:
print "Error: ", ex
try:
f = Function('f', IntSort(), IntSort())
print get_models(f(x) == x, 10)
except Z3Exception as ex:
print "Error: ", ex
答案 1 :(得分:2)
下面的python函数是同时包含常量和函数的公式模型的生成器。
search
答案 2 :(得分:1)
引用 http://theory.stanford.edu/~nikolaj/programmingz3.html#sec-blocking-evaluations
def all_smt(s, initial_terms):
def block_term(s, m, t):
s.add(t != m.eval(t))
def fix_term(s, m, t):
s.add(t == m.eval(t))
def all_smt_rec(terms):
if sat == s.check():
m = s.model()
yield m
for i in range(len(terms)):
s.push()
block_term(s, m, terms[i])
for j in range(i):
fix_term(s, m, terms[j])
for m in all_smt_rec(terms[i:]):
yield m
s.pop()
for m in all_smt_rec(list(initial_terms)):
yield m
这确实从 Leonardo 自己的答案中表现得更好(考虑到他的答案很旧)
start_time = time.time()
v = [BitVec(f'v{i}',3) for i in range(6)]
models = get_models([Sum(v)==0],8**5)
print(time.time()-start_time)
#211.6482105255127s
start_time = time.time()
s = Solver()
v = [BitVec(f'v{i}',3) for i in range(6)]
s.add(Sum(v)==0)
models = list(all_smt(s,v))
print(time.time()-start_time)
#13.375828742980957s
就我所观察到的,将搜索空间拆分为不相交的模型会产生巨大的差异