function Z = ECGModel(X,Phasemn)
% Z = ECGModel(X,Phaemn)
% Overview: Generate Synthetic ECG beat using parameters defined in X over phase
% defined in the Phasemn variable.
%
% Inputs:
%           X - contains the amplitude (alphai), standard deviation (bi) and phase (tetai) for
%           each Gaussian function used for generating the synthetic ECG beat.
%           
%           Phasemn - array contains the phase points over which synthetic
%           ECG beat is generated.
%
% Outputs:
%           Z - synthetic ECG beat generated using Gaussian parameter estimates.
%
% Open Source ECG Toolbox, version 1.0, November 2006
% Released under the GNU General Public License
% Copyright (C) 2006  Reza Sameni
% Sharif University of Technology, Tehran, Iran -- LIS-INPG, Grenoble, France
% reza.sameni@gmail.com
% Last modified:
% on 11/30/2020 by Ismail Sadiq
%
% TODO: Return the analytic Jacobians to accelerate the convergence of the
% nonlinear least squares solver. Added on Feb. 2019
%
% 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 2 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, write to the Free Software
% Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.

L = (length(X)/3);

alphai = X(1:L);
bi = X(L+1:2*L);
tetai = X(2*L+1:3*L);

Z = zeros(size(Phasemn));
for j = 1:length(alphai),
    dtetai = rem(Phasemn - tetai(j) + pi,2*pi)-pi;
    Z = Z + alphai(j) .* exp(-dtetai .^2 ./ (2*bi(j) .^ 2));
end
