Theta function: Special functions that arise in the study of quadratic forms and partition theory, commonly employed to express series identities in number theory.

The statistical physics of graphs and partition functions represents a vibrant intersection of graph theory, statistical mechanics and computational complexity.

Eugene P. Wigner, On a Class of Analytic Functions from the Quantum Theory of Collisions, Annals of Mathematics, Vol. 53, No. 1 (Jan., 1951), pp. 36-67 ...