Let $A$ be a positive definite, real $n \times n$ matrix. This defines a norm on $\mathbb{R}^n$. Now I have a given point $p \in \mathbb{R}^n$ and I want to find the lattice point $x \in \mathbb{Z}^n$ that is closest to $p$ with respect to this norm. This is commonly known as the **Closest Vector Problem** (CVP) and seems to be very important. So I guess algorithms to solve this should be implemented somewhere. However, I was not able to find something.

Is this there a package for solving this problem for some common mathematical software like Maple, Mathematica, Sage, etc?

Note that I am not interested in some approximation using LLL or so, I want really the (or one) closest vector!