function [YtY,XtY,YtX,XtX,Y,X] = var_sample_moments(FirstObservation,LastObservation,qlag,var_trend_order);
global options_

X = [];
Y = [];
YtY = [];
YtX = [];
XtY = [];
XtX = [];

if exist(options_.datafile)
  eval(options_.datafile);
else
  eval(['load ' options_.datafile]);
end

data = [ ];
for i=1:size(options_.varobs,1)
  data = [data eval(deblank(options_.varobs(i,:)))];
end

if qlag > FirstObservation
  disp('VarSampleMoments :: not enough data to initialize! Try to increase FirstObservation.')
  return
end
NumberOfObservations = LastObservation-FirstObservation+1;
NumberOfVariables = size(data,2);
if var_trend_order == -1% No constant
    X = zeros(NumberOfObservations,NumberOfVariables*qlag);
elseif var_trend_order == 0% Constant
  X = zeros(NumberOfObservations,NumberOfVariables*qlag+1);
  indx = NumberOfVariables*qlag+1:NumberOfVariables*qlag+NumberOfVariables;
elseif var_trend_order == 1;% Constant + Trend
  X = zeros(NumberOfObservations,NumberOfVariables*qlag+2);
  indx = NumberOfVariables*qlag+1:NumberOfVariables*qlag+2;
else
  disp('var_sample_moments :: trend must be equal to -1,0 or 1!')
  return
end
% I build matrices Y and X  
Y = data(FirstObservation:LastObservation,:);
for t=1:NumberOfObservations
  line = t + FirstObservation-1;
  for lag = 1:qlag
    X(t,(lag-1)*NumberOfVariables+1:lag*NumberOfVariables) = data(line-lag,:);
  end
  if var_trend_order == 0
    X(t,indx) = ones(1,NumberOfVariables);
  elseif var_trend_order == 1
  X(t,indx) = [ 1 , t ];
  end
end

YtY = Y'*Y;
YtX = Y'*X;
XtY = X'*Y;
XtX = X'*X;