ADDED   mttroot/mtt/lib/control/PPP/ppp_are.m
Index: mttroot/mtt/lib/control/PPP/ppp_are.m
==================================================================
--- /dev/null
+++ mttroot/mtt/lib/control/PPP/ppp_are.m
@@ -0,0 +1,25 @@
+function [P,A_u,A_w,k] = ppp_are (A,B,C,D,Q,R)
+
+  ## usage:  [P,A_u,A_w] = ppp_are (A,B,C,D,Q,R)
+  ##
+  ## 
+
+
+  ## Steady-state Linear Quadratic solution
+  ## using Algebraic Riccati equation (ARE)
+  Q_x =  C'*Q*C;			# Weighting on x
+  [k, P, poles] = lqr (A, B, Q_x, R); # Algebraic Riccati solution
+
+  ## Basis functions
+  A_u = compan(poly(poles));
+
+  ## Avoid spurious imag parts due to rounding
+  A_u = real(A_u);		
+
+  ## Setpoint basis functions
+  A_w = 0;
+
+  ## Include A_w in A_u
+  A_u = ppp_aug(A_u,A_w);
+
+endfunction