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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*.
SMA* has the following properties
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. [1]
Pseudo code:
functionsimplememoryboundedA*-star(problem):pathqueue:setofnodes,orderedbyf-cost;beginqueue.insert(problem.root-node);whileTruedobeginifqueue.empty()thenreturnfailure;//there is no solution that fits in the given memorynode:=queue.begin();// min-f-cost-nodeifproblem.is-goal(node)thenreturnsuccess;s:=next-successor(node)if!problem.is-goal(s)&&depth(s)==max_depththenf(s):=inf;// there is no memory left to go past s, so the entire path is uselesselsef(s):=max(f(node),g(s)+h(s));// f-value of the successor is the maximum of// f-value of the parent and // heuristic of the successor + path length to the successorendififnomoresuccessorsthenupdatef-costofnodeandthoseofitsancestorsifneededifnode.successors⊆queuethenqueue.remove(node);// all children have already been added to the queue via a shorter wayifmemoryisfullthenbeginbadNode:=shallowestnodewithhighestf-cost;forparentinbadNode.parentsdobeginparent.successors.remove(badNode);ifneededthenqueue.insert(parent);endforendifqueue.insert(s);endwhileend
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