Reciprocity

Reciprocity may refer to:

Law and trade

Reciprocity (Canadian politics), free trade with the United States of America
- Reciprocal trade agreement, entered into in order to reduce (or eliminate) tariffs, quotas and other trade restrictions on items traded between the signatories
Interstate reciprocity, recognition of sibling federated states' laws:
- In the United States specifically:
  - Full Faith and Credit Clause, which provides for it
- Occupational licensing, which in some jurisdictions provides for it
Traffic violations reciprocity where non-resident drivers are treated like residents
Quid pro quo, a legal concept of the exchange of good or services, each having value

Norm of reciprocity, social norm of in-kind responses to the behavior of others
Reciprocity (cultural anthropology), way of defining people's informal exchange of goods and labour
Reciprocity (evolution), mechanisms for the evolution of cooperation
Reciprocity (international relations), principle that favours, benefits, or penalties that are granted by one state to the citizens or legal entities of another, should be returned in kind
Reciprocity (social and political philosophy), concept of reciprocity as in-kind positive or negative responses for the actions of others
Reciprocity (social psychology), in-kind positively or negatively connoted responses of individuals towards the actions of others
Ethic of reciprocity (the Golden Rule), that one should treat others as one would like others to treat oneself
Serial reciprocity, in which the benefactor of a gift or service will in turn provide benefits to a third party

Reciprocity (engineering), used in the analysis of structures and to resolve complex load conditions
Reciprocity (electromagnetism), theorems relating sources and the resulting fields in classical electromagnetism
Reciprocity (electrical networks), reciprocity theorem as it relates to current and voltage in electrical networks
Reciprocity (network science), measures the tendency of vertex pairs to form mutual connections between each other
Reciprocity (optoelectronic), a diode under illumination to the photon emission of the same diode under applied voltage
Reciprocity (photography), the relationship between the intensity of the light and duration of the exposure that result in identical exposure
Reciprocity of twist and wrench, in screw theory
Reciprocity theorem (disambiguation), several unrelated results
Reciprocity of antenna transmitting and receiving characteristics
Helmholtz reciprocity, linear propagation.

Reciprocity law (law of reciprocity) in mathematics, including
- Quadratic reciprocity, a fundamental result in number theory
- Cubic reciprocity, theorems that state conditions under which the congruence x³ ≡ p (mod q) is solvable
- Quartic reciprocity, a collection of theorems in elementary and algebraic number theory that state conditions under which the congruence x⁴ ≡ p (mod q) is solvable
- Artin reciprocity law, a general theorem in number theory that provided a partial solution to Hilbert's ninth problem
- Reciprocity relation or exact differential, a mathematical differential of the form dQ, for some differentiable function Q
Weil reciprocity law
Reciprocal polynomials, the coefficients of the remainder polynomial are the bits of the CRC
Reciprocal square root
Reciprocity (projective geometry), a collineation from a projective space onto its dual space, taking points to hyperplanes (and vice versa) and preserving incidence
Frobenius reciprocity, from group representation theory
Reciprocity law for Dedekind sums
Stanley's reciprocity theorem, states that a certain functional equation is satisfied by the generating function of any rational cone and the generating function of the cone's interior
Hermite reciprocity for invariants of binary forms.