--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/toolbox/makejcf.m	Wed May 06 14:56:53 2015 +0200
@@ -0,0 +1,39 @@
+function A = makejcf(n, e, m, X)
+%MAKEJCF   A matrix with given Jordan canonical form.
+%          MAKEJCF(N, E, M) is a matrix having the Jordan canonical form
+%          whose i'th Jordan block is of dimension M(i) with eigenvalue E(i),
+%          and where N = SUM(M).
+%          Defaults: E = 1:N, M = ONES(SIZE(E)) with M(1) so that SUM(M) = N.
+%          The matrix is constructed by applying a random similarity
+%          transformation to the Jordan form.
+%          Alternatively, the matrix used in the similarity transformation
+%          can be specified as a fifth parameter.
+%          In particular, MAKEJCF(N, E, M, EYE(N)) returns the Jordan form
+%          itself.
+%          NB: The JCF is very sensitive to rounding errors.
+
+if nargin < 2, e = 1:n; end
+if nargin < 3, m = ones(size(e)); m(1) = m(1) + n - sum(m); end
+
+if any( size(e(:)) ~= size(m(:)) )
+   error('Parameters E and M must be of same dimension.')
+end
+
+if sum(m) ~= n, error('Block dimensions must add up to N.'), end
+
+A = zeros(n);
+j = 1;
+for i=1:max(size(m))
+    if m(i) > 1
+        Jb = jordbloc(m(i),e(i));
+    else
+        Jb = e(i);  % JORDBLOC fails in n = 1 case.
+    end
+    A(j:j+m(i)-1,j:j+m(i)-1) = Jb;
+    j = j + m(i);
+end
+
+if nargin < 4
+   X = randn(n);
+end
+A = X\A*X;