ComplexPairingSum

Base class: ComplexBaseSum

The PairingSum operator is parametrized by a sparse matrix $P(i,j)$ of size $L \times L$. Each entry $P(i,j)$ for $i < j$ corresponds to the operator $P(i,j) f_i^\dagger f_j^\dagger$, whilst each entry $P(i,j)$ for $i > j$ corresponds to the operator $P(i,j) f_i f_j$. The PairingSum operator represents the sum $\sum_{i<j}P_{i,j}f_i^{\dagger}f_j^{\dagger} + \sum_{i>j}P_{i,j}f_if_j$