So I’ve been trying to wrap my head around this particular piece of information:
I understand what h_l^T h_l and h_c^T h_c do and how to apply the resulting matrices. However, I do not understand how the author arrived at the ‘unseparable’ matrices in (3.6). Reading the references paper  did not help too much.
Is anyone here who can clear up the confusion, and possibly show me how this could be extended to even larger filters (just for fun)?