The unimodular equivalence of sublattices in an $n$-dimensional lattice

Abstract

In this paper, we study the unimodular equivalence of sublattices in an $n$-dimensional lattice. A recursive procedure is given to compute the cardinalities of the unimodular equivalent classes with the indices which are powers of a prime $p$. We also show that these are integral polynomials in $p$. When $n=2$, the explicit formulae of the cardinalities are presented depending on the prime decomposition of the index $m$. We also give an explicit formula on the number of co-cyclic sublattices with a fixed index $m$, which consist a unimodular equivalent class of sublattices.