Cameron, In your example, I think P is the only matrix with 0-1 entries that has the given row and column sums.
In general, I would solve the problem simulating a Markov Chain. Start from a given incidence matrix A and iterate the following steps: (1) select two rows, a, b, and two columns, i, j, at random. (2) If A[c(a,b), c(i,j)] is of one of the forms 1 0 or 0 1 0 1 1 0 then set it to the other, i.e. set A[c(a,b), c(i,j)] <- A[c(b,a), c(i,j)]. After sufficiently many iterations, A will have a uniform distribution. Giovanni > Date: Thu, 19 Oct 2006 15:49:55 -0400 > From: "Guenther, Cameron" <[EMAIL PROTECTED]> > Sender: [EMAIL PROTECTED] > Precedence: list > Thread-topic: [R] randomize a matrix > Thread-index: Acbzt8BjJUXZEHZgQNaMi9gYYuh3Sg== > > Hello everyone, > > If I have an incidence matrix of 0 and 1's > > P=[1 1 1 1 1 1 > 1 1 1 1 0 0 > 1 1 1 0 0 0 > 1 1 1 0 0 0 > 1 1 0 0 0 0] > > I want to create a new uniform random matrix [a] that is filled with 0's > and 1's but constrained so that the row and column sums are the same as > in [P]. Does anyone know how to accomplish this? > > Thanks in advance > > Cameron Guenther, Ph.D. > Associate Research Scientist > FWC/FWRI, Marine Fisheries Research > 100 8th Avenue S.E. > St. Petersburg, FL 33701 > (727)896-8626 Ext. 4305 > [EMAIL PROTECTED] > > ______________________________________________ > R-help@stat.math.ethz.ch mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > > -- __________________________________________________ [ ] [ Giovanni Petris [EMAIL PROTECTED] ] [ Department of Mathematical Sciences ] [ University of Arkansas - Fayetteville, AR 72701 ] [ Ph: (479) 575-6324, 575-8630 (fax) ] [ http://definetti.uark.edu/~gpetris/ ] [__________________________________________________] ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.