Lenstra–Lenstra–Lovász lattice basis reduction algorithm

The Lenstra–Lenstra–Lovász (LLL) lattice basis reduction algorithm is a polynomial time lattice reduction algorithm invented by Arjen Lenstra, Hendrik Lenstra and László Lovász in 1982. Given a basis ${\displaystyle \mathbf {B} =\{\mathbf {b} _{1},\mathbf {b} _{2},\dots ,\mathbf {b} _{d}\}}$ with n-dimensional integer coordinates, for a lattice L (a discrete subgroup of Rⁿ) with ${\displaystyle d\leq n}$, the LLL algorithm calculates an LLL-reduced (short, nearly orthogonal) lattice basis in time

where ${\displaystyle B}$ is the largest length of ${\displaystyle \mathbf {b} _{i}}$ under the Euclidean norm, that is, ${\displaystyle B=\max \left(\|\mathbf {b} _{1}\|_{2},\|\mathbf {b} _{2}\|_{2},\dots ,\|\mathbf {b} _{d}\|_{2}\right)}$.

The original applications were to give polynomial-time algorithms for factorizing polynomials with rational coefficients, for finding simultaneous rational approximations to real numbers, and for solving the integer linear programming problem in fixed dimensions.