Persi Diaconis and Bernd Sturmfels have an article on generating random contingency tables uniformly distributed subject to having fixed marginals for the same purpose (null distribution of conditional test) and they used Markov Chain Monte Carlo to sample. That could perhaps be adapted here. The article is in Annals of Statistics from several years ago, and if you google for "algebraic statistics" you'll probably find several recent expositions of the ideas, possibly even code.
Reid Huntsinger -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Michela Marignani Sent: Thursday, January 27, 2005 3:52 AM To: [email protected] Subject: [R] Request for help My name is Michela Marignani and I'm an ecologist trying to solve a problem linked to knight' s tour algorithm. I need a program to create random matrices with presence/absence (i.e. 1,0 values), with defined colums and rows sums, to create null models for statistical comparison of species distribution phenomena. I've seen on the web many solutions of the problem, but none provides the freedom to easily change row+colums constraint and none of them produce matrices with 1 and 0. Also, I've tryied to use R, but it is too complicated for a not-statistician as I am....can you help me? Thank you for your attention, so long Michela Marignani University of Siena Environmental Science Dept. Siena, Italy [EMAIL PROTECTED] ______________________________________________ [email protected] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html ______________________________________________ [email protected] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
