Computation of disconnected contributions to nucleon observables

We compare several methods for computing disconnected fermion loops contributing to nucleon three-point functions. The comparison is carried out using one ensemble of $N_f=2+1+1$ twisted mass fermions with pion mass of 373 MeV. The complete set of operators up to one-derivative are examined by developing optimized code for mutli-GPUs. Simple guidelines are given as to the preferable method for each class of operators.