LLL candidate conjecture for modular symbols

Let v=[v1,,vn]{\mathbf v}=[v_1,\dots,v_n] be a modular symbol with v>1\|{\mathbf v}\|>1, and define

b(v)=ivivit.b({\mathbf v})=\sum_i v_i v_i^t.

Let EE be the standard basis of Zn{\mathbb Z}^n. The quadratic form b(v)b({\mathbf v}) is called LLL-reduced when it is the Gram matrix of an LLL-reduced ordered basis. Let candv\operatorname{cand}{\mathbf v} be the set of nonzero lattice points that can be written as w=iqiviw=\sum_i q_i v_i with 0qi<10\leq |q_i|<1. LLL candidate conjecture. If b(v)b({\mathbf v}) is an LLL-reduced quadratic form, then

candvE.\operatorname{cand}{\mathbf v}\cap E\ne\varnothing.

This conjecture offers an alternative, potentially efficient way to choose candidates for the modular symbol algorithm and is intended to give an explicit polynomial-time implementation. Its validity is presented as conjectural, with no resolution supplied in the paper.

Sources & referencesView supporting material

Primary source

Paul E. Gunnells, “Computing Hecke eigenvalues below the cohomological dimension”, arXiv:math/9811134 (1999).

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