function trend = lineartrend(o) % --*-- Unitary tests --*--
% Returns a trend centered on zero.
%
% INPUTS
% - o [dseries] time series with T observations.
%
% OUTPUTS
% - trend [double] T*1 vector, linear trend with mean zero.
%
% REMARKS
% the generic element of the returned argument is trend(i) = i - (n+1)/2.
% Copyright (C) 2017 Dynare Team
%
% This file is part of Dynare.
%
% Dynare is free software: you can redistribute it and/or modify
% it under the terms of the GNU General Public License as published by
% the Free Software Foundation, either version 3 of the License, or
% (at your option) any later version.
%
% Dynare is distributed in the hope that it will be useful,
% but WITHOUT ANY WARRANTY; without even the implied warranty of
% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
% GNU General Public License for more details.
%
% You should have received a copy of the GNU General Public License
% along with Dynare. If not, see .
trend = transpose(1:o.nobs)-.5*(o.nobs+1);
return
%@test:1
a = dseries(randn(100,3));
try
trend = a.lineartrend;
t(1) = 1;
catch
t(1) = 0;
end
if t(1)
t(2) = abs(mean(trend))<1e-12;
end
T = all(t);
%@eof:1