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MATRICESTOTALLYPOSITIVERELATIVETOATREE ELA

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ELA

MATRICES TOTALLY POSITIVE RELATIVE TO A TREE

CHARLES R. JOHNSON, ROBERTO S. COSTAS-SANTOS, AND BORIS TADCHIEV§

Abstract. It is known that for a totally positive (TP) matrix, the eigenvalues are positive and distinct and the eigenvector associated with the smallest eigenvalue is totally nonzero and has an alternating sign pattern. Here, a certain weakening of the TP hypothesis is shown to yield a similar conclusion.

Key words. Totally positive matrices, Sylvester’s identity, Graph theory, Spectral theory.

AMS subject classifications.15A18, 94C15.

Received by the editors November 1, 2007. Accepted for publication March 22, 2009. Handling Editor: Bryan L. Shader. This research was conducted during the summer of 2007 as part of the College of William and Mary REU program and was supported by NSF grant DMS-03-53510.

Department of Mathematics, College of William and Mary, Williamsburg, VA 23187 ([email protected]).

Department of Mathematics, College of William and Mary, Williamsburg, VA 23187

([email protected]). The research of RSCS has been supported by Direcci´on General de Inves- tigaci´on del Ministerio de Educaci´on y Ciencia of Spain under grant MTM 2006-13000-C03-02.

§Undergraduate, Binghamton University, Binghamton, NY 13902 ([email protected]).

Electronic Journal of Linear Algebra ISSN 1081-3810 A publication of the International Linear Algebra Society Volume 18, pp. 211-221, April 2009

http://math.technion.ac.il/iic/ela

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