I have a distance matrix with more than 1M nodes. I wonder whether there exist any Neighbour Joining implementation which could calculate a tree structure within a reasonable amount of time. The complexity for Neighbour Joining is N^3, so I am not sure whether there is any heuristic algorithm could do this.
Currently, I have a distance matrix. If there is another comparable tree building algorithm starting from distance matrix, I would like to try that method also.