MATLAB高手,请问谁能帮忙解释以下程序的含义,

MATLAB高手,请问谁能帮忙解释以下程序的含义,
% EDGE4CONNECTED Creates edges where each node
% is connected to its four adjacent neighbors on a
% height x width grid.
% E - a vector in which each row i represents an edge E(i,1) --> E(i,2).
% The edges are listed is in the following neighbor order:
% down,up,right,left,where nodes indices are taken column-major.
function E = edges4connected(height,width)
N = height*width;
I = []; J = [];
% connect vertically (down,then up)
is = [1:N]'; is([height:height:N])=[];
js = is+1;
I = [I;is;js];
J = [J;js;is];
% connect horizontally (right,then left)
is = [1:N-height]';
js = is+height;
I = [I;is;js];
J = [J;js;is];
E = [I,J];
end
PS：is = [1:N]'; is([height:height:N])=[];
I = [I;is;js];都是什么意思啊?