Index: mttroot/mtt/bin/trans/m/sm2ir.m
==================================================================
--- mttroot/mtt/bin/trans/m/sm2ir.m
+++ mttroot/mtt/bin/trans/m/sm2ir.m
@@ -1,11 +1,25 @@
 function [Y,X] = sm2ir(A,B,C,D,T,u0,x0);
+% sm2ir - Constrained-state matrix to impulse response.
+%
+%     %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
+%     %%%%% Model Transformation Tools %%%%%
+%     %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+% 
+% Matlab function  sm2ir
 % [Y,X] = sm2ir(A,B,C,D,T,u0,x0);
-% Constrained-state matrix to impulse response.
 % A,B,C,D,E - (constrained) state matrices
 % T vector of time points
-% u0 input gain vector: u = u0*unit step.
+% u0 input gain vector: u = u0*unit impulse.
+
+
+% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+% %% Version control history
+% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+% %% $Id$
+% %% $Log$
+% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 
 
 [Ny,Nu] = size(D);
 [Ny,Nx] = size(C);
 
@@ -32,16 +46,21 @@
 
 one = eye(Nx);
 
 Y = zeros(N,Ny);
 X = zeros(N,Nx);
+
+dt = T(2)-T(1);% Assumes fixed interval
+expAdt = expm(A*dt); % Compute matrix exponential
+expAt = one;
 i = 0;
+x = (B*u0+x0);
 for t = T'
   i=i+1;
   if Nx>0
-    expAt = expm(A*t);
-    x = expAt*(B*u0+x0);
+    % expAt = expm(A*t);
+    x = expAdt*x;
     X(i,:) = x';
     if Ny>0
       y = C*x;
       Y(i,:) = y';
     end;