function [Y,X] = sm2ir(A,B,C,D,T,u0,x0);
% [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.
[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);
i = 0;
for t = T'
i=i+1;
if Nx>0
expAt = expm(A*t);
x = expAt*(B*u0+x0);
X(i,:) = x';
if Ny>0
y = C*x;
Y(i,:) = y';
end;
end;
end;