# Column subset selection is NP-complete

## TL;DR

This paper proves that the column subset selection problem (CSSP), a fundamental problem in numerical linear algebra, is NP-complete, resolving a long-standing open question about its computational complexity.

## Contribution

The paper establishes that CSSP is NP-complete, providing the first proof of its computational hardness and clarifying the problem's algorithmic intractability.

## Key findings

- CSSP is NP-complete.
- Addresses a long-standing open problem.
- Implications for algorithms in numerical linear algebra.

## Abstract

Let $M$ be a real $r\times c$ matrix and let $k$ be a positive integer. In the column subset selection problem (CSSP), we need to minimize the quantity $\|M-SA\|$, where $A$ can be an arbitrary $k\times c$ matrix, and $S$ runs over all $r\times k$ submatrices of $M$. This problem and its applications in numerical linear algebra are being discussed for several decades, but its algorithmic complexity remained an open issue. We show that CSSP is NP-complete.