function [Y,X] = sm2ir(A,B,C,D,T,u0,x0);
% sm2ir - state matrix to impulse response.
%
% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% %%%%% Model Transformation Tools %%%%%
% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
% Matlab function sm2ir
% [Y,X] = sm2ir(A,B,C,D,T,u0,x0);
% A,B,C,D,E - (constrained) state matrices
% T vector of time points
% u0 input gain vector: u = u0*unit impulse.
% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% %% Version control history
% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% %% $Id$
% %% $Log$
% %% Revision 1.3 1996/12/05 10:17:34 peterg
% %% Put in version control history.
% %%
% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
[Ny,Nu] = size(D);
[Ny,Nx] = size(C);
if max(max(abs(D)))~=0
mtt_info('D matrix non-zero - ignoring');
end;
if nargin<6
u0 = zeros(Nu,1);
u0(1) = 1;
end;
if nargin<7
x0 = zeros(Nx,1);
end;
[N,M] = size(T);
if M>N
T = T';
N = M;
end;
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 = expAdt*x;
x = expm(A*t)*(B*u0+x0);
X(i,:) = x';
if Ny>0
y = C*x;
Y(i,:) = y';
end;
end;
end;