function [xP] = predict_grad(xP,G,rx,lamda)
%This rouine uses the gradient descent algorithm to try to help
%'push' particles to a region of higher probability before the 
%state update equation
global Npart

if nargin == 3, lamda = 0.1; end;
for r = 1:Npart,
    %get better estimate for xP's
    P = xP(:,:,r);
    P = P + 2*lamda*(rx-P*G)*G';  %Gradient of observation equation
    xP(:,:,r) = P;
end