例如，top-down 解析器可以确保找到每一个可能的产品，但 可能会非常慢，因为要频繁地（指数级）进行回溯。

For example, top-down parsers are guaranteed to find every possible production, but can be extremely slow because of frequence (exponention order) backtracking.

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Packrat解析解决了诸如指数级解析时间的问题。

Packrat parsing solves the problem of this kind of parser, i.e. exponential parse time.

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刚性飞片在炸药爆炸作用下的一维抛掷问题，仅当爆炸气体多方指数等于三时可以求得解析解；

The one-dimensional problem of the motion of the rigid plate under explosive attack has an analytic solution only when the polytropic index of detonation product equals to three.

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