Terminology and Notation
- the branching factor of a search tree
- the cost associated with moving from node to node
- the cost from the root to the node
- the heuristic estimate of the distance between the node and the goal
- the start state
- the goal state (sometimes, not to be confused with the function)
- the current search direction. By convention, is equal to 1 for the forward direction and 2 for the backward direction (Kwa 1989)
- the opposite search direction (i.e. )
- the search tree in direction d. If, the root is, if, the root is
- the leaves of (sometimes referred to as ). It is from this set that a node is chosen for expansion. In bidirectional search, these are sometimes called the search 'frontiers' or 'wavefronts', referring to how they appear when a search is represented graphically. In this metaphor, a 'collision' occurs when, during the expansion phase, a node from one wavefront is found to have successors in the opposing wavefront.
- the non-leaf nodes of . This set contains the nodes already visited by the search
Read more about this topic: Bidirectional Search, Description