function z = prob_grooteman_12_series2_x2z_test(varargin)
%% settings

OPT = struct(...
    'U1', [],...
    'U2', []...
    );

OPT = setproperty(OPT, varargin{:});

%% limit state function

z1  = 2-OPT.U2+exp(-0.1*(OPT.U1.^2))+(0.2*OPT.U1).^4;
z2  = 4.5-OPT.U1.*OPT.U2;
z   = min([z1, z2], [], 2);