Clean namespaces, especially for RiemannianMetric

[ninamiolane]

Where should the content be modified?

No response

What should be modified?

After discussion with @LPereira95 The attributes and methods of a class should be cleaned, e.g.:

Move RiemannianMetric's

• closest neighbor
• distance pairwise
  to another place

Move SymmetricMatrices':

• apply_to_eigenvalues

Discuss where to put:

• powerm/power
• expm goes in the backend, but Matrices.group_exp calls it

symmetric matrices is not a group thus can't have group exp, it would call the backend's expm if it needs it, because the alternative: symmetric_matrices.embedding_space.group_exp is too long and potentially not necessary. (to confirm with @ythanwerdas ).

Similar question for how to handle linear algebra computations in SymmetricMatrices: for example, use a flag is_sym that is a string, but also have a check flag that is False by default, but can be changed for development, when we actually want to check whether the input matrix is really symmetric/spd.

Note: numpy/scipy might have this type of flag system (or alternatively, several functions) to handle this linear algebra: maybe look at what they do, and follow for ease of Api.

Additional information

No response