Rankin–Cohen bracket

In mathematics, the Rankin–Cohen bracket of two modular forms is another modular form, generalizing the product of two modular forms. Rankin (1956, 1957) gave some general conditions for polynomials in derivatives of modular forms to be modular forms, and Cohen (1975) found the explicit examples of such polynomials that give Rankin–Cohen brackets. They were named by Zagier (1994), who introduced Rankin–Cohen algebras as an abstract setting for Rankin–Cohen brackets.