(-(((x).^2)/5+((1-y).^2)/2+((0.5-z).^2)/3))...
    -4*exp(-(((2-x).^2)/2+((-1-y).^2)/5+((-1.5-z).^2)/2));
X = (rand(3,50)-0.5)*6;
y = groundtruth(X(1,:),X(2,:),X(3,:))+1e-2*randn(1,size(X,2));

[xeva yeva zeva] = meshgrid(-3:0.5:3,-3:0.5:3,-3:0.2:3);
xstar = [xeva(:)';yeva(:)';zeva(:)'];

figure; scatter3(X(1,:),X(2,:),X(3,:),40,y,'filled')
xlabel('x');ylabel('y');zlabel('z'); title('Training Data')

pause
%% Set up Gaussian process

% Use a standard GP regression model:
GP = tacopig.gp.Regressor;

% Plug i