SMA*

SMA* or Simplified Memory Bounded A* is a shortest path algorithm based on the A* algorithm. The main advantage of SMA* is that it uses a bounded memory, while the A* algorithm might need exponential memory. All other characteristics of SMA* are inherited from A*.

Properties
SMA* has the following properties


 * It works with a heuristic, just as A*
 * It is complete if the allowed memory is high enough to store the shallowest solution
 * It is optimal if the allowed memory is high enough to store the shallowest optimal solution, otherwise it will return the best solution that fits in the allowed memory
 * It avoids repeated states as long as the memory bound allows it
 * It will use all memory available
 * Enlarging the memory bound of the algorithm will only speed up the calculation
 * When enough memory is available to contain the entire search tree, then calculation has an optimal speed

Implementation
The implementation of Simple memory bounded A* is very similar to that of A*; the only difference is that nodes with the highest f-cost are pruned from the queue when there isn't any space left. Because those nodes are deleted, simple memory bounded A* has to remember the f-cost of the best forgotten child of the parent node. When it seems that all explored paths are worse than such a forgotten path, the path is regenerated.

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