The dimension of the largest tensors in D is of the order O ( M ⋅ ⋅ χ χ 2 ) ; when constructing the Θ Θ α α γ γ i j one makes the summation over β β , m and n for each γ γ , α α , i , j , adding up to a total of O ( M 4 ⋅ ⋅ χ χ 3 ) operations. The same holds for the formation of the elements ρ ρ γ γ γ γ ′ j j ′ , or for computing the left-hand eigenvectors λ λ β β ′ | Φ Φ β β ′ [ J C ] ⟩ ⟩ , a maximum of O ( M 3 ⋅ ⋅ χ χ 3 ) , respectively O ( M 2 ⋅ ⋅ χ χ 3 ) basic operations. In the case of qubits, M = 2 , hence its role is not very relevant for the order of magnitude of the number of basic operations, but in the case when the on-site dimension is higher than two it has a rather decisive contribution.