Measuring the fluctuation-dissipation ratio in glassy systems with no perturbing field

A method is presented for measuring the integrated response in Ising spin system without applying any perturbing field. Large-scale simulations are performed in order to show how the method works. Very precise measurements of the fluctuation-dissipation ratio are presented for 3 different Ising models: the 2-dimensional ferromagnetic model, the mean-field diluted 3-spin model, and the 3-dimensional Edwards-Anderson model.