code: def choose_insertsize(readlen=150, step=20, cutoff=.01):
      
      print("Insert-size\tOverlap", file=sys.stderr)
      for i in range(0, 3 * readlen, step):
          p = gaussian_prob_le(i, i / 5, 2 * readlen)
          if p < cutoff or p > 1 - cutoff:
              continue
          print("{0}bp\t{1}%".format(i, int(round(100 * p))), file=sys.stderr)
docs: Calculate ratio of overlap for a range of insert sizes. Idea borrowed from
      ALLPATHS code (`allpaths_cache/CacheToAllPathsInputs.pl`).