For some reason, your code in the 2nd stage doesn't fold the communities correctly. I've tested with the data from the "Louvain" paper (Figure 1), by the end of the first iteration of first stage, I got six separated communities, which were {1,2,4}, {0,3,5,7}, {6}, {8,15},{9,12,14}, {10,11,13}. However, for certain vertex, let's say "7" from the group of {0,3,5,7} was computed "deltaQ" with vertex "3" instead of {6} in the second stage.
For some reason, your code in the 2nd stage doesn't fold the communities correctly. I've tested with the data from the "Louvain" paper (Figure 1), by the end of the first iteration of first stage, I got six separated communities, which were {1,2,4}, {0,3,5,7}, {6}, {8,15},{9,12,14}, {10,11,13}. However, for certain vertex, let's say "7" from the group of {0,3,5,7} was computed "deltaQ" with vertex "3" instead of {6} in the second stage.
But the final result was correct.