Index: mttroot/mtt/lib/control/PPP/ppp_are.m
==================================================================
--- mttroot/mtt/lib/control/PPP/ppp_are.m
+++ mttroot/mtt/lib/control/PPP/ppp_are.m
@@ -11,15 +11,27 @@
   
   if nargin<7
     A_type = "feedback";
   endif
   
-
+  [n_x,n_u,n_y] = abcddim(A,B,C,D); # Dimensions
+  n_q = is_square(Q);		# Size of Q
+  if n_q==0
+    error("Q must be square");
+  endif
+  
   ## 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
+  if n_q==n_y			# Output weight
+    Q_x =  C'*Q*C;		# Weighting on x
+  elseif n_q==n_x		# State weight
+    Q_x = Q;
+  else
+    error(sprintf("Q (%ix%i) must be %ix%i or %ix%i",n_q,n_q,n_y,n_y,n_x,n_x));
+  endif
+  Q_x
+  [k, P, poles] = lqr (A, B, Q_x, R) # Algebraic Riccati solution
 
   ## Basis functions
   if strcmp(A_type,"companion")
     A_u = compan(poly(poles));
   elseif strcmp(A_type,"feedback")