Filtering assumes Hermitian/symmetric Laplacian

[iglesias]

compute_fourier_basis uses scipy.linalg.eigh assuming the matrix is complex Hermitian or real symmetric. This will lead to incorrect results, if I am not mistaken, when using for example the directed cycle graph (aka directed Ring or Path simple graph).

I am wondering if this is intended, for instance the library only supports filtering on non-directed graphs, or if there's anything else. Thank you in advance for any help!