Constrained Process Near the Critical Point

Processes of constant entropy, volume and polarization of a combined system of a lattice and an ordering system in the classical potential are calculated. In an isentropic process, the first order transition does not take place if the coexistence line is not parallel to the temperature axis. An expected double hysteresis loop just above the transition point may or may not appear depending upon the lattice heat capacity in an isentropic process. The three types of relaxation after constrained processes are discussed in parallel, with connection to the critical slowing down.