Z3/Python 从模型中获取 python 值 [英] Z3/Python getting python values from model
问题描述
如何从 Z3 模型中获取真正的 Python 值?
How can I get real python values from a Z3 model?
例如
p = Bool('p')
x = Real('x')
s = Solver()
s.add(Or(x < 5, x > 10), Or(p, x**2 == 2), Not(p))
s.check()
print s.model()[x]
print s.model()[p]
打印
-1.4142135623?
False
但那些是 Z3 对象而不是 python float/bool 对象.
but those are Z3 objects and not python float/bool objects.
我知道我可以使用 is_true
/is_false
检查布尔值,但是我如何优雅地将整数/实数/...例如,通过字符串并删除这个额外的 ?
符号).
I know that I can check boolean values using is_true
/is_false
, but how can I elegantly convert ints/reals/... back to usable values (without going through strings and cutting away this extra ?
symbol, for example).
推荐答案
对于布尔值,您可以使用函数 is_true
和 is_false
.数值可以是整数、有理数或代数.我们可以使用函数is_int_value
、is_rational_value
和is_algebraic_value
来测试每种情况.整数情况是最简单的,我们可以使用as_long()
方法将Z3整数值转换为Python long.对于有理值,我们可以使用numerator()
和denominator()
方法来获得代表分子和分母的Z3 个整数.方法 numerator_as_long()
和 denominator_as_long()
是 self.numerator().as_long()
和 self.denominator().as_long()
.最后,代数数用于表示无理数.AlgebraicNumRef
类有一个名为 approx(self, precision)
的方法.它返回一个 Z3 有理数,它以 1/10^precision
的精度逼近代数数.这是有关如何使用此方法的示例.它也可以在网上获得:http://rise4fun.com/Z3Py/Mkw
For Boolean values, you can use the functions is_true
and is_false
. Numerical values can be integer, rational or algebraic. We can use the functions is_int_value
, is_rational_value
and is_algebraic_value
to test each case. The integer case is the simplest, we can use the method as_long()
to convert the Z3 integer value into a Python long. For rational values, we can use the methods numerator()
and denominator()
to obtain the Z3 integers representing the numerator and denominator. The methods numerator_as_long()
and denominator_as_long()
are shortcuts for self.numerator().as_long()
and self.denominator().as_long()
. Finally, algebraic numbers are used to represent irrational numbers. The AlgebraicNumRef
class has a method called approx(self, precision)
. It returns a Z3 rational number that approximates the algebraic number with precision 1/10^precision
. Here is an example on how to use this methods. It is also available online at: http://rise4fun.com/Z3Py/Mkw
p = Bool('p')
x = Real('x')
s = Solver()
s.add(Or(x < 5, x > 10), Or(p, x**2 == 2), Not(p))
s.check()
m = s.model()
print m[p], m[x]
print "is_true(m[p]):", is_true(m[p])
print "is_false(m[p]):", is_false(m[p])
print "is_int_value(m[x]):", is_int_value(m[x])
print "is_rational_value(m[x]):", is_rational_value(m[x])
print "is_algebraic_value(m[x]):", is_algebraic_value(m[x])
r = m[x].approx(20) # r is an approximation of m[x] with precision 1/10^20
print "is_rational_value(r):", is_rational_value(r)
print r.numerator_as_long()
print r.denominator_as_long()
print float(r.numerator_as_long())/float(r.denominator_as_long())
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