“…The upsampling operators are based on hierarchical clustering algorithms [15], [23]- [25] so that, in contrast with [26], matrix inversions are not required, avoiding the related numerical issues. Our work is substantially different from [15], [16], which deal with graph encoder-decoder architectures. On top of our theoretical analysis and extensive numerical simulations, additional differences to prior work are that: (a) our graph decoder is an untrained network, and thus, it does not need a training phase; (b) we only require a decoder-like architecture for denoising graph signals, so it is not necessary to jointly design and train two different architectures as done in [15], [16].…”