# etree

## Purpose

Elimination tree of a matrix.

## Synopsis

    p = etree(A)
    p = etree(A,'col')
    [p,q] = etree(...)

## Description

`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.

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

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

## Examples

    etreeplot(sprandsym(50, 0.1))

## References

[1] John R. Gilbert, Cleve Moler and Robert Schreiber, "Sparse Matrices in MATLAB: Design and Implementation," SIAM Journal on Matrix Analysis and Applications 13, pp. 333-356, Jan. 1992.

(c) Copyright 1994 by The MathWorks, Inc.