function [ fm ] = gsp_modulate( G,f,k )
%GSP_MODULATE Generalized modulation of the signal f to the frequency k
% Usage: fm = gsp_modulate( G,f,k );
%
% Input parameters
% G : Graph
% f : Signal (column)
% k : Indices of frequencies (int)
% Output parameters
% fm : Modulated signal
%
% This function modulate the column vector f onto the node i. If f is a
% matrix, the modulation will be applicated to each column.
%
%
% Url: https://epfl-lts2.github.io/gspbox-html/doc/operators/gsp_modulate.html
% Copyright (C) 2013-2016 Nathanael Perraudin, Johan Paratte, David I Shuman.
% This file is part of GSPbox version 0.7.5
%
% This program 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.
%
% This program 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 this program. If not, see <http://www.gnu.org/licenses/>.
% If you use this toolbox please kindly cite
% N. Perraudin, J. Paratte, D. Shuman, V. Kalofolias, P. Vandergheynst,
% and D. K. Hammond. GSPBOX: A toolbox for signal processing on graphs.
% ArXiv e-prints, Aug. 2014.
% http://arxiv.org/abs/1408.5781
% Author: Nathanael Perraudin
% Date : 09.12.2013
nt = size(f,2);
fm = sqrt(G.N)*repmat(f,1,nt).*repmat(G.U(:,k+1),1,nt);
end