MathDB
Conditional Matrices

Source: 2009 MMO Problem #3

September 12, 2011
linear algebramatrixcombinatorics unsolvedcombinatorics

Problem Statement

Decide whether the integers 1,2,,1001,2,\ldots,100 can be arranged in the cells C(i,j)C(i, j) of a 10×1010\times10 matrix (where 1i,j101\le i,j\le 10), such that the following conditions are fullfiled: i) In every row, the entries add up to the same sum SS. ii) In every column, the entries also add up to this sum SS. iii) For every k=1,2,,10k = 1, 2, \ldots, 10 the ten entries C(i,j)C(i, j) with ijkmod10i-j\equiv k\bmod{10} add up to SS. (Proposed by Gerhard Woeginger, Austria)