Potential bug of hyperboloid frechet mean

[ljxw88]

Applying frechet mean on the Lorentz model with K not equal to -1 cannot get the correct answer.

I found the bug in frechetmean/forward/hyperboloid_forward.py. Where the original code calculate variable mu with
mu = u / torch.sqrt(K * Lorentz._ldot(u, u, keepdim=True))

Changing it to
mu = - K * u / torch.sqrt(K * Lorentz._ldot(u, u, keepdim=True))
solves the problem.