说明：   Tree Decomposition. [NODE_FINAL,VX,VY]=TREE_DECOMPOSITION(N) finds the circular shaped nodes generating 3-tree decomposition. Total number of nodes are restricted to be 1, 3, 6, 12, 24, etc. Extra nodes will be disregarded. For example, given input nodes are 100, then only 96 nodes are used to generate tree decomposition and the rest 4 nodes are disregarded. The main area of using this code is the area of smart grid.