** Elimination tree of a matrix. **

** p = etree(A) returns an elimination tree for the square **

** symmetric matrix whose upper triangle is that of A. **

** p(j) is the parent of column j in the tree, **

** or 0 if j is a root. **

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** p = etree(A,'col') returns the elimination tree of A'*A. **

** p = etree(A,'sym') is the same as p = etree(A). **

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** [p,q] = etree(...) also returns a postorder permutation q on the tree. **

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** See also TREELAYOUT , TREEPLOT , ETREEPLOT . **

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