if (0 <= ptrA[reflayer] && ptrA[reflayer] < notr[reflayer])
trkRA = (AliTRDtrackletGTU*) fZChannelTracklets[reflayer][zch].At(ptrA[reflayer]);
else {
if (0 <= ptrA[reflayer] && ptrA[reflayer] < notr[reflayer])
trkRA = (AliTRDtrackletGTU*) fZChannelTracklets[reflayer][zch].At(ptrA[reflayer]);
else {