
Archives
 December 2017
 November 2017
 October 2017
 September 2017
 August 2017
 July 2017
 June 2017
 May 2017
 April 2017
 March 2017
 February 2017
 January 2017
 December 2016
 November 2016
 October 2016
 September 2016
 August 2016
 July 2016
 June 2016
 May 2016
 April 2016
 March 2016
 February 2016
 January 2016
 December 2015
 November 2015
 October 2015
 September 2015
 August 2015
 July 2015
 June 2015
 May 2015
 April 2015
 March 2015
 February 2015
 January 2015
 December 2014
 November 2014
 October 2014
 September 2014
 August 2014
 July 2014
 June 2014
 May 2014
 April 2014
 March 2014
 February 2014
 January 2014
 December 2013
 November 2013
 October 2013
 September 2013
 June 2013
 May 2013
 April 2013
 March 2013
 February 2013
 January 2013
 December 2012
 November 2012
 October 2012
 September 2012
 August 2012
 July 2012
 May 2012
 March 2012
 February 2012
 January 2012
 December 2011
 November 2011
 October 2011

Meta
Monthly Archives: December 2012
Symmetric 01 Matrices with All Eigenvalues Positive
Recently I was surprised to learn that the only symmetric 01 matrix with all eigenvalues positive is the identity matrix. Here’s a very nice proof of this fact given in this answer of Robert Israel’s: Let A be an symmetric 01 matrix … Continue reading
Posted in linear algebra, matrices
Leave a comment
The Absorption Identity for Binomial Coefficients
The absorption identity for binomial coefficients is This post will give a couple of proofs of the identity and then use it to prove some other identities involving binomial coefficient sums. Proofs of the absorption identity Proof 1: Use the … Continue reading
Posted in binomial coefficients, combinatorics
3 Comments
Some Uses of Duality in Linear Programming
For most of my students, the first time they see duality in linear programming their first reaction is “What’s the big deal?” There was a recent post on math.SE asking the same question. Duality in linear programming seems to me … Continue reading
Posted in linear programming
1 Comment