Non maximal suppression in object detection

Hi, what is the difference between y2 = boxes(:,4) and s = boxes(:,end) in the following nms code?

function top = nms(boxes, overlap) % top = nms_fast(boxes, overlap) % Non-maximum suppression. (FAST VERSION) % Greedily select high-scoring detections and skip detections % that are significantly covered by a previously selected % detection. % NOTE: This is adapted from Pedro Felzenszwalb's version (nms.m), % but an inner loop has been eliminated to significantly speed it % up in the case of a large number of boxes % Tomasz Malisiewicz (<mailto:[e-mail] [e-mail]>)

if isempty(boxes) top = []; return; end

x1 = boxes(:,1); y1 = boxes(:,2); x2 = boxes(:,3); y2 = boxes(:,4); s = boxes(:,end);

area = (x2-x1+1) .* (y2-y1+1); [vals, I] = sort(s);

pick = s*0; counter = 1; while ~isempty(I)

last = length(I);
i = I(last);  
pick(counter) = i;
counter = counter + 1;

xx1 = max(x1(i), x1(I(1:last-1)));
yy1 = max(y1(i), y1(I(1:last-1)));
xx2 = min(x2(i), x2(I(1:last-1)));
yy2 = min(y2(i), y2(I(1:last-1)));

w = max(0.0, xx2-xx1+1);
h = max(0.0, yy2-yy1+1);

o = w.*h ./ area(I(1:last-1));

I([last; find(o>overlap)]) = [];
end

pick = pick(1:(counter-1)); top = boxes(pick,:);

[Image Analyst]

http://www.mathworks.com/matlabcentral/answers/13205-tutorial-how-to-format-your-question-with-markup