In mathematics, the Maass–Selberg relations are some relations describing the inner products of truncated real analytic Eisenstein series, that in some sense say that distinct Eisenstein series are orthogonal.
Hans Maass introduced the Maass–Selberg relations for the case of real analytic Eisenstein series on the upper half plane.
[1] Atle Selberg extended the relations to symmetric spaces of rank 1.
Informally, the Maass–Selberg relations say that the inner product of two distinct Eisenstein series is zero.
However the integral defining the inner product does not converge, so the Eisenstein series first have to be truncated.