dcomplex attempt() {
auto k = config->perturbation_order();
if (k <= 0) return 0; // Config is empty, trying to remove makes no sense
int p = rng(k); // Choose one of the operators for removal
auto det_ratio = config->Mmatrices[up].try_remove(p, p) * config->Mmatrices[down].try_remove(p, p);
return -k / (beta * U) * det_ratio; // The Metropolis ratio
}
dcomplex attempt() { // Insert an interaction vertex at time tau with aux spin s
double tau = rng(beta);
int s = rng(2);
auto k = config->perturbation_order();
auto det_ratio = config->Mmatrices[up].try_insert(k, k, {tau, s}, {tau, s}) * config->Mmatrices[down].try_insert(k, k, {tau, s}, {tau, s});
return -beta * U / (k + 1) * det_ratio; // The Metropolis ratio
}
