  In this paper we study phase transitions for weakly interacting multiagent
systems. By investigating the linear response of a system composed of a finite
number of agents, we are able to probe the emergence in the thermodynamic limit
of a singular behaviour of the susceptibility. We find clear evidence of the
loss of analyticity due to a pole crossing the real axis of frequencies. Such
behaviour has a degree of universality, as it does not depend on either the
applied forcing nor on the considered observable. We present results relevant
for both equilibrium and nonequilibrium phase transitions by studying the
Desai-Zwanzig and Bonilla-Casado-Morillo models.
