Since the solution \( \Psi_{\lambda} \) seldomly can be found in closed form, approximations are sought. In this text we define an approximative wave function or an ansatz to the exact wave function as $$ \Phi_{\lambda}=\Phi_{\lambda}(x_1,x_2,\dots,x_A), $$ with $$ \Phi_{0}=\Phi_{0}(x_{1},x_{2},\dots,x_{A}), $$ being the ansatz for the ground state.