MathDB
Finite Operations on Matrix

Source: Singapore Mathematical Olympiad 2014 Senior Section Round 2

March 1, 2019
linear algebramatrixcombinatorics

Problem Statement

In the following 6×66\times 6 matrix, one can choose any k×kk\times k submatrix, with 1<k61<k\leq6 and add 11 to all its entries. Is it possible to perform the operation a finite number of times so that all the entries in the 6×66\times 6 matrix are multiples of 33?
(201020020120102020010220111120000000) \begin{pmatrix} 2 & 0 & 1 & 0 & 2 & 0 \\ 0 & 2 & 0 & 1 & 2 & 0 \\ 1 & 0 & 2 & 0 & 2 & 0 \\ 0 & 1 & 0 & 2 & 2 & 0 \\ 1 & 1 & 1 & 1 & 2 & 0 \\ 0 & 0 & 0 & 0 & 0 & 0 \end{pmatrix}
Note: A p×qp\times q submatrix of a m×nm\times n matrix (with pmp\leq m, qnq\leq n) is a p×qp\times q matrix formed by taking a block of the entries of this size from the original matrix.