Apply single IFO cut only when more than 2 IFOs are used by PyGRB

bin/pycbc_multi_inspiral

@@ -709,7 +709,7 @@ with ctx:
                     # indices from that IFO, i.e., IFO 0; otherwise, this
                     # method finds coincidences and applies the single IFO cut,
                     # namely, triggers must have at least 2 IFO SNRs above
-                    # args.sngl_snr_threshold.
+                    # args.sngl_snr_threshold when 3 or more IFOs are involved.
                     if nifo > 1:
                         coinc_idx = coh.get_coinc_indexes(
                             idx_dict, time_delay_idx[slide][position_index]

pycbc/events/coherent.py

@@ -59,9 +59,11 @@ def get_coinc_indexes(idx_dict, time_delay_idx):
                 [coinc_list, idx_dict[ifo] - time_delay_idx[ifo]]
             )
     # Search through coinc_idx for repeated indexes. These must have been loud
-    # in at least 2 detectors.
+    # in at least 2 detectors if the analysis uses more than 2 detectors.
     counts = np.unique(coinc_list, return_counts=True)
-    coinc_idx = counts[0][counts[1] > 1]
+    coinc_idx = (
+        counts[0][counts[1] > 1] if len(idx_dict.keys()) > 2 else counts[0]
+    )
     return coinc_idx