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The problem of interest is $$ \min_{x\in\mathbb{Z}^n} \frac{1}{2}x^\top Q x + c^\top x $$ where $Q$ is a positive definite matrix. I am reasonably sure this can't be solved in poly-time, since the closest lattice vector problem (in $\ell_2$ norm) can be reformulated in the above form. Do we have a proof of $\mathsf{NP}$-hardness for a corresponding decision problem - does there exist $x\in\mathbb{Z}^n$ so that the above quadratic takes a value less than or equal to $f^* \in \mathbb{R}$?

I don't find a proof of $\mathsf{NP}$-hardness of the closest lattice vector problem in $\ell_2$ norm. If such a proof is found, then this problem is solved.

Inuyasha Yagami
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Sriram
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1 Answers1

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The closest lattice vector problem is NP-hard in the $L_2$ norm. See NP completeness of closest vector problem for a reference to the proof.

D.W.
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