Only just figured it out.
The first and second columns are the new group number after clustering.
4 elements in x each was given a group number from 1 to 4.
The system will then group element 1 and 2 in x together and give a new group number '5'.
The system will then group element 6 and 8 in x together and give a new group number '6'.
The system will at last group '5' and '6' together while group 5 looks like (1,2), and group 6 looks like (6,8).
the third column is the distance between the two group.
first number in column 3 is 1, that is the difference between elements 1 and 2.
second number in column 3 is 2, that is the difference between elements 6 and 8.
third number in column 3 is 4. That is the tricky one. group 5 and group 6 would look like (1,2) and (6,8). Matlab use the shortest euclidean distance by default. Therefore the shortest between two groups will be the 2 from group 5 and the 6 from group 6 with the distance 6-2=4.
Ta-da!
