E2pq

E2pq is a term that appears in several disciplines as a compact notation for a quantity depending on two parameters, p and q. There is no single, universally accepted definition of E2pq; its precise meaning is determined by context and field of study. In mathematics and theoretical computer science, E2pq is often encountered as a two-variable function or bilinear form, where p and q denote parameters, variables, or indices. In such uses, E2pq may be defined within a particular model or formula, for example as part of a polynomial expansion, an energy-like term, or a score function over pairs of items. In physics and chemistry, E2pq can appear as a shorthand for a two-particle interaction energy or an exchange term involving two components labeled p and q; again, the exact definition depends on the model.

The term tends to be applied when a calculation or equation involves pairs of elements and a second-order or pairwise interaction is significant. The ambiguity means that E2pq should be understood with reference to the surrounding definitions in the source text. In published work, E2pq is usually introduced with a concrete definition, followed by properties, special cases, and examples. Because the notation is not standardized, readers should consult the specific context to determine what E2pq represents in a given article or study.

See also: E2, PQ, bilinear form, two-variable function.