  Exact diagonalization (ED) is one of the most reliable and established
numerical methods of quantum many-body theory. The main limiting factor of the
method is the exponential scaling of Hilbert space dimension with system size.
Fortunately, by symmetry considerations the effective dimension can be reduced
by multiple orders of magnitude. Here, we present lattice-symmetries, a package
for working with such symmetry-adapted quantum many-body bases and operators.
It supports bases for spin-1/2 particles with arbitrary user-defined symmetries
and generic 1-, 2-, 3-, and 4-point operators. As an example application we
discuss SpinED program which allows to easily diagonalize clusters of at least
42 sites on a single node thus making large-scale ED easily accessible to
people with no background in numerical methods and computational physics.
