**3. Opposition-Based ACO**

The method of construction opposite path based on OBL is given in this section. At the same time, in order to use the opposite path information, three kinds of frameworks of opposite-based ACO algorithms including ACO-Index, ACO-MaxIt, and ACO-Rand will also be proposed. In order to unify the content, the construction method of the opposite path will be combined with the specific algorithm. Details will be given in the following subsections.
