Users:Orange Quail 9

$[asy] /* Made by MRENTHUSIASM */ size(300); pair A, B, C, D; A = (-400,100); B = (0,100); C = (400,100); D = (0,-300); dot("$\hat{f}(i-1,j)$",A,1.5*dir(A),linewidth(4)); dot("$\hat{f}(i,j)$",B,1.5*dir(B),linewidth(4)); dot("$\hat{f}(i+1,j)$",C,1.5*dir(C),linewidth(4)); dot("$\hat{f}(i,j+1)$",D,1.5*dir(D),linewidth(4)); draw(A--B^^B--D^^C--B); [/asy]$