Fig. 2: Interaction graph for a transverse field Ising model.
From: Practical Hamiltonian learning with unitary dynamics and Gibbs states

Interaction graph \({{{{{{{\mathcal{G}}}}}}}}\) for a 9-qubit transverse field Ising model. The degree of this Hamiltonian is \({{{{{{{\mathscr{D}}}}}}}}=4\), since for instance P2 is connected to 4 other Pauli terms.