Graph multiresolution: largest_eigenvector

[mys007]

I think the behavior on L141 in gsp_graph_multiresolution.m is wrong in the case when largest_eigenvector(1)==0, which now leads to filling largest_eigenvector with 0s as sign(0)=0. I suggest L141 being executed only if largest_eigenvector(1)~=0.
Also, as eig works up to eps precision, one should IMHO have nonnegative_logicals=(largest_eigenvector >= -eps); instead of nonnegative_logicals=(largest_eigenvector >= 0);, as the current may lead to problems with graphs with multiple connected components, which are then numerically not properly identified to be kept, which may lead to NaNs in Kron reduction.

[mdeff]

Thanks for reporting the issue. Note however that this toolbox is not developed nor maintained anymore. Please consider using the pygsp instead.

[mys007]

Thanks for your reply! When/if I come back to Kron reduction again, I will definitely use the new Python toolbox (looks very nice, great work) and I will check if my two issues are still relevant there.

[mdeff]

Thanks :) I think they'll be relevant, though I did not touch the graph multiresolution code (it was initially translated from matlab by interns). Please submit a PR if you come across them again.