message: Change DCA calc to O(N) vs O(N^2)
diff: @@ -664,11 +664,10 @@ Long_t AliAnalysisTaskWeakDecayVertexer::Tracks2V0vertices(AliESDEvent *event) {
  if (esdTrack->GetTPCNcls() < 70 && lThisTrackLength<80 &&fkExtraCleanup ) continue;
  Double_t d=esdTrack->GetD(xPrimaryVertex,yPrimaryVertex,b);
  - if (TMath::Abs(d)<fV0VertexerSels[2]) continue;
  - if (TMath::Abs(d)>fV0VertexerSels[6]) continue;
  - if (esdTrack->GetSign() < 0.) neg[nneg++]=i;
  - else pos[npos++]=i;
  + //Select on single-track to PV DCA here, do not call that O(N^2)
  + if (esdTrack->GetSign() < 0. && TMath::Abs(d)<fV0VertexerSels[1]) neg[nneg++]=i;
  + if (esdTrack->GetSign() > 0. && TMath::Abs(d)<fV0VertexerSels[2]) pos[npos++]=i;
  }
  for (i=0; i<nneg; i++) {
  @@ -686,9 +685,6 @@ Long_t AliAnalysisTaskWeakDecayVertexer::Tracks2V0vertices(AliESDEvent *event) {
  Double_t lNegMassForTracking = ntrk->GetMassForTracking();
  Double_t lPosMassForTracking = ptrk->GetMassForTracking();
  - if (TMath::Abs(ntrk->GetD(xPrimaryVertex,yPrimaryVertex,b))<fV0VertexerSels[1])
  - if (TMath::Abs(ptrk->GetD(xPrimaryVertex,yPrimaryVertex,b))<fV0VertexerSels[2]) continue;
  -
  fHistV0Statistics->Fill(1.5); //pass distance to PV
  AliExternalTrackParam nt(*ntrk), pt(*ptrk);
  