--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/toolbox/cycol.m	Thu May 07 18:36:24 2015 +0200
@@ -0,0 +1,22 @@
+function A = cycol(n, k)
+%CYCOL   Matrix whose columns repeat cyclically.
+%        A = CYCOL([M N], K) is an M-by-N matrix of the form A = B(1:M,1:N)
+%        where B = [C C C...] and C = RANDN(M, K).  Thus A's columns repeat
+%        cyclically, and A has rank at most K.   K need not divide N.
+%        K defaults to ROUND(N/4).
+%        CYCOL(N, K), where N is a scalar, is the same as CYCOL([N N], K).
+%
+%        This type of matrix can lead to underflow problems for Gaussian
+%        elimination: see NA Digest Volume 89, Issue 3 (January 22, 1989).
+
+m = n(1);              % Parameter n specifies dimension: m-by-n.
+n = n(max(size(n)));
+
+if nargin < 2, k = max(round(n/4),1); end
+
+A = randn(m, k);
+for i=2:ceil(n/k)
+    A = [A A(:,1:k)];
+end
+
+A = A(:, 1:n);