# Correct: keepdim=True → (2, 1) broadcasts against (2, 3)
normed = m / m.sum(dim=1, keepdim=True)
print(normed)
# tensor([[0.1667, 0.3333, 0.5000],
#         [0.2667, 0.3333, 0.4000]])
print(normed.sum(dim=1))   # tensor([1., 1.]) — every row sums to 1 ✅