Petri网定向展开的hmax启发式函数实现正确性求证

我基于一篇论文实现了用于Petri网定向展开的hmax启发式函数，该函数用于估算从一个标识（参数a）到另一个标识（参数b）的剩余距离。目前无法自行复现验证，需要协助确认实现的正确性与假设合理性。

相较于论文定义，我做了如下修改：

• 因采用基于代价的定向展开，引入了cost_function
• 为避免递归计算时出现循环，用in_stack跟踪调用路径，检测到循环时返回inf
• 新增if len(possible_candidates) == 0: return 0的逻辑，但不确定该假设是否正确，也不清楚possible_candidates为何会为空

实现代码如下：

def compute_hmax(
    self,
    mark: frozenset[PetriNet.Place],
    target: Set[PetriNet.Place],
    cost_function,
):
    if len(mark) == 0:
        self.local_configuration.hmax = 0
    else:
        in_stack = (
            dict()
        )  # stack to detect visited nodes in the search to detect cycles
        d = self.hmax(mark, frozenset(target), in_stack, cost_function)
        self.local_configuration.hmax = d

@cached(
    cache={},
    key=lambda self, a, b, in_stack, cost_function: hashkey((a, b)),
)
def hmax(
    self,
    a: frozenset[PetriNet.Place],
    b: frozenset[PetriNet.Place],
    in_stack,
    cost_function,
):
    if b.issubset(a):
        return 0

    elif len(b) == 1:
        q = list(b)[0]

        if q in in_stack:
            return float("inf")  # cycle detected

        in_stack[q] = True

        pre_trans = set(map(lambda arc: arc.source, q.in_arcs))

        possible_candidates = list(
            map(
                lambda t: (
                    t,
                    self.hmax(
                        a, frozenset(t.preset), in_stack, cost_function
                    ),
                ),
                pre_trans,
            )
        )

        in_stack.pop(q)

        if len(possible_candidates) == 0:
            return 0

        min_d_tup = min(possible_candidates, key=lambda t: t[1] + cost_function[t[0]])

        return cost_function[min_d_tup[0]] + min_d_tup[1]

    else:
        return max(
            list(
                map(
                    lambda t: self.hmax(
                        a, frozenset({t}), in_stack, cost_function
                    ),
                    b,
                )
            )
        )

内容的提问来源于stack exchange，提问作者Ariba Siddiqui