def alexander_polynomial(braid, t=t, modulus=None, seifert=False):
""" Calculate Alexander Polynomial."""
if seifert:
M = Matrix(seifert_matrix(braid).tolist())
if modulus is None:
apoly = M - t*M.transpose()
else:
apoly = (M - t*M.transpose()) % modulus
apoly = apoly.det()
else:
deleted = False
h = generators(braid)
M = alexander_matrix(braid, t, modulus)
for i in range(len(braid)):
if h[i] == 0:
deleted = True
M.row_del(i)
M.col_del(i)
break
if not deleted:
M.row_del(-1)
M.col_del(-1)
apoly = M.det()
return _normalize_apoly(apoly)
