function [Y,X] = sm2ir(A,B,C,D,T,u0,x0);
% sm2ir - Constrained-state matrix to impulse response.
%
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%     %%%%% Model Transformation Tools %%%%%
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% 
% 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.


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% %% $Log$
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[Ny,Nu] = size(D);
[Ny,Nx] = size(C);

if max(max(abs(D)))~=0
  mtt_info('D matrix non-zero - ignoring');

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;
  end;
end;