function Xk = ekf_cost(X,params)
% X: state vector
% params: a cell containing all parameters required:
% W: process noise vector
% nk: a vector indicating the number of Gaussian Kernels used for modeling
% each independent component
% fs:sampling frequency
L=size(X,1); % number of states in the state vector X
W= params{1};
nk= params{2};
fs= params{3};
Lind = length(nk); % number of independent components used for MECG cancellation
w=W(1); % average heart-rate in rads
dt= 1/fs;
Xk=zeros(L,1);
Xk(1) = X(1) + w*dt; % theta state variable
if(Xk(1) > pi)
Xk(1) = Xk(1) - 2*pi;
end
ptr=1; % pointer to the current parameter extracted from the W vector
for i=1:Lind
kernelParam = reshape(W(ptr+1:ptr+nk(i)*3),3,[]); % kernel parameters for the current independent component
alpha= kernelParam(1,:);
theta= kernelParam(2,:);
b= kernelParam(3,:);
dtheta = rem(Xk(1) - theta, 2*pi);
Xk(i+1) = X(i+1) - dt*sum(w*alpha./(b.^2).*dtheta.*exp(-dtheta.^2./(2*b.^2))); % s state variables
ptr=ptr+nk(i)*3;
end
end