MathDB
System of linear equations in a square grid

Source: Austrian-Polish 2005, Problem 8

July 5, 2015
functionsquare gridalgebralinear equation

Problem Statement

Given the sets Rmn={(x,y)x=0,1,,m;y=0,1,,n}R_{mn} = \{ (x,y) \mid x=0,1,\dots,m; y=0,1,\dots,n \}, consider functions f:Rmn{1,0,1}f:R_{mn}\to \{-1,0,1\} with the following property: for each quadruple of points A1,A2,A3,A4RmnA_1,A_2,A_3,A_4\in R_{mn} which form a square with side length 0<s<30<s<3, we have f(A1)+f(A2)+f(A3)+f(A4)=0.f(A_1)+f(A_2)+f(A_3)+f(A_4)=0. For each pair (m,n)(m,n) of positive integers, determine F(m,n)F(m,n), the number of such functions ff on RmnR_{mn}.