Feynman-Graph Expansion for the Equation of State near the Critical Point (Ising-like Case)

The scaling equation of state of an Ising-like ferromagnet is derived by an expansion in ɛ=4-d, where d is the dimension of space. The result is compared with numerical calculations on the three-dimensional Ising model. It is also established that the "linear model" is exact up to order ɛ².