“…where A * a , B * a , C * a , D * a , and E * a are individual trainable graph convolutions with filter coefficients that are trainable parameters with subscript a indicating trainable, and NN u (⋅) and NN r (⋅) are two neural networks, which involve trainable parameters. Intuitively, (3a) and (3b) are neural-network implementations of (2a) and (2b), respectively, replacing fixed graph convolutions h * v by trainable graph convolutions A * a ; and (3c) and (3d) are neural-network implementations of the proximal functions (2c) and (2d), respectively, using neural networks to solve sub-optimization problems; see similar substitutions in [14,15,16]. Instead of following the exact mathematical relationship in (2), we allow trainable operators to adaptively learn from data, usually reducing a lot of computation.…”