Your code is correct. This produces all pairs in variable "pairs". A distance function is usually symmetric, so the the distance between last row and first row d(1,r) should be the same as the distance between first row and last row d(r,1). So it is ok that test each pair only once:
r = 8; pairs = [];
for i=1:r,
for n = i+1:r,
pairs(end+1, :) = [i n],
end
end
You can also use nchoosek to generate the pairs and then loop over the number of pairs
pairs2 = nchoosek(1:r, 2)
If you want to test all combinations, you just have to change the second for loop to
for n = 1:r
