有关matlab的sum函数问题,其中sum（x,y）的表示方法是什么意思?急用n=10;z = zeros(n,n);cells = z;cells(n/2,.25*n:.75*n) = 1;cells(.25*n:.75*n,n/2) = 1;x = 2:n-1;y = 2:n-1;sum(x,y) = cells(x,y-1) + cells(x,y+1) + ...cells(x-1,y) + c