From dcc7c7e1f0209179eda7a355c82b3bdb3da485e2 Mon Sep 17 00:00:00 2001
From: michel <michel@ac1d8469-bf42-47a9-8791-bf33cf982152>
Date: Mon, 8 May 2006 14:51:06 +0000
Subject: [PATCH] 3 v4: chnaged lyapunov_symm.m to work with 6.5 except with
 unit roots

git-svn-id: https://www.dynare.org/svn/dynare/dynare_v4@740 ac1d8469-bf42-47a9-8791-bf33cf982152
---
 matlab/lyapunov_symm.m | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/matlab/lyapunov_symm.m b/matlab/lyapunov_symm.m
index 1c1be1e16..dbcacf89c 100644
--- a/matlab/lyapunov_symm.m
+++ b/matlab/lyapunov_symm.m
@@ -14,10 +14,21 @@ function [x,ns_var]=lyapunov_symm(a,b)
     e1 = abs(my_ordeig(t)) > 2-options_.qz_criterium;
   end
   k = sum(e1);
-  [u,t] = ordschur(u,t,e1); 
-  n = length(e1)-k;
-  b=u(:,k+1:end)'*b*u(:,k+1:end);
-  t = t(k+1:end,k+1:end);
+  if exist('ordschur','builtin')
+    % selects stable roots
+    [u,t] = ordschur(u,t,e1); 
+    n = length(e1)-k;
+    b=u(:,k+1:end)'*b*u(:,k+1:end);
+    t = t(k+1:end,k+1:end);
+  elseif k > 0
+    % problem for Matlab version that don't have ordschur
+    error(['lyapunov_sym: you need a Matlab version > 6.5 to handle models' ...
+	   ' with unit roots'])
+  else
+    % no unit root
+    n = length(e1);
+    b=u'*b*u;
+  end
   x=zeros(n,n);
   for i=n:-1:2
     if t(i,i-1) == 0