mc_weight_type Try() {
#ifdef DEBUG
std::cout << "I AM IN Try for Remove_Cdag_C_Delta_SegmentPicture" << std::endl;
std::cout << "CONFIG BEFORE: " << Config.DT << std::endl;
for (int a = 0; a<Config.Na; ++a) print_det(Config.dets[a]);
#endif
// the det pointer has to be recomputed each time, since global moves will change it
det = Config.dets[a_level];
// Pick up a couple of C, Cdagger to remove at random
const int Na(det->size());
if (Na==0) return 0;
// I am selecting the n th C or Cdag operator, starting from small time.
// Because the det orders the tau in decreasing order (cf insert)
// I need to iterate over the C, Cdag in reverse.
int n = Random(2*Na); // pick up n
// the Cs will look like 0 : c1 c2 c1 c2 c1 c2 c1 c2 : beta
// where c1, c2 are C,Cdag or Cdag,C
// from n, I now compute the number of the c1,c2 operator (between 0 and N-1)
// if n = 2p, n1 = p , n2 = p
// if n = 2p+1, n1 = p +1 , n2 = p
// e.g. c1[0] c2[0] c1[1] c2[1] c1[2] c2[2] c1[3] c2[3]
// n= 0 1 2 3 4 5 6 7
//eg n=2,p=1 { }
//eg n=3,p=1 { }
//eg n=7,p=3 } { // be careful of the cyclic condition
int n1 = 1+ (n+1)/2, n2 = 1 + n/2;
const bool use_cyclicity (n1 > Na);
if (use_cyclicity) n1 = 1; // cyclic condition
// decide whether C1 is C or Cdag
bool Cisfirst = (det->Cdagger_rbegin()->tau > det->C_rbegin()->tau );
int numC = (Cisfirst ? n1: n2);
int numCdag = (Cisfirst ? n2: n1);
#ifdef DEBUG
cout<<" Cfirst n n1 n2 "<< Cisfirst<< " "<<n<< " "<< n1 << " "<< n2 <<endl;
cout<<numC<< " "<<numCdag <<endl;
#endif
// take an iterator on the couple C,Cdag
Configuration::DET_TYPE::Cdagger_reverse_iterator itCdag = det->select_reverse_Cdagger( numCdag );
Configuration::DET_TYPE::C_reverse_iterator itC = det->select_reverse_C( numC );
// Remove the operators from the traces
Config.DT.removeTwoOperators(*itCdag,*itC);
// first_point is the first of the couple, next_point is the op on a_level *after* the second
// with cyclicity
// if cyclicity was not used, the first point is simply the lowest tau
// otherwise it is the *highest* tau !
Configuration::OP_REF first_point, next_point;
const bool C_before_Cdag(((*itC)->tau < (*itCdag)->tau));
if ((!use_cyclicity && C_before_Cdag) || (use_cyclicity && !C_before_Cdag)) {
first_point = *itC;
++itC;
next_point = (itC == det->C_rend() ? *det->C_rbegin() : *itC); // cyclicity check
}
else {
first_point = *itCdag;
++itCdag;
next_point = (itCdag == det->Cdagger_rend() ? *det->Cdagger_rbegin() : *itCdag); // cyclicity check
}
double length_max = ( first_point == next_point ? Config.Beta :
Config.CyclicOrientedTimeDistance(next_point->tau- first_point->tau) );
// Acceptance probability
mc_weight_type p = Config.DT.ratioNewTrace_OldTrace() * det->try_remove(Na-numCdag, Na-numC);
double Tratio = (Na ==1 ? 1 : 2*Na) / (Config.Beta * length_max);
// (Na term : because if we have only 1 couple of C Cdagger, n = 0 and 1 will lead to the same couple
// and this is the only case like this.
#ifdef DEBUG
cout<< " length_max "<<length_max<<endl;
std::cout << "RATIO: " << Config.DT.ratioNewTrace_OldTrace() << std::endl;
std::cout << "CONFIG AFTER: " << Config.DT << std::endl;
#endif
return p*Tratio;
}
