fix: Empty connection sets

bsb_nest/connection.py

@@ -69,6 +69,8 @@ def create_connections(self, simdata, pre_nodes, post_nodes, cs):
                 pre_nodes, post_nodes, cs
             ):
                 MPI.barrier()
+                if len(pre_locs) == 0 or len(post_locs) == 0:
+                    continue
                 cell_pairs, multiplicity = np.unique(
                     np.column_stack((pre_locs[:, 0], post_locs[:, 0])),
                     return_counts=True,
@@ -95,7 +97,8 @@ def predict_mem_iterator(self, pre_nodes, post_nodes, cs):
         predicted_all_mem = (
             len(pre_nodes) * 8 * 2 + len(post_nodes) * 8 * 2 + len(cs) * 6 * 8 * (16 + 2)
         ) * MPI.get_size()
-        predicted_local_mem = predicted_all_mem / len(cs.get_local_chunks("out"))
+        n_chunks = len(cs.get_local_chunks("out"))
+        predicted_local_mem = (predicted_all_mem / n_chunks) if n_chunks > 0 else 0.0
         if predicted_local_mem > avmem / 2:
             # Iterate block-by-block
             return self.block_iterator(cs)

tests/test_nest.py

@@ -1,4 +1,5 @@
 import unittest
+from unittest.mock import patch
 
 import nest
 import numpy as np
@@ -98,6 +99,18 @@ def spy(_):
         self.assertGreaterEqual(err_mean, abs(mean_rate - expected_rate))
         self.assertGreaterEqual(err_var, var_rate - expected_var)
 
+    @patch("bsb_hdf5.connectivity_set.ConnectivitySet.get_local_chunks")
+    def test_regression_issue_9(self, get_content_mock):
+        # Override get_local_chunks to test empty connection sets
+        get_content_mock.return_value = []
+        cfg = get_test_config("gif_pop_psc_exp")
+        # we delete the NEST connectivity rule
+        cfg.simulations["test_nest"].connection_models["gif_pop_psc_exp"].rule = None
+        network = Scaffold(cfg, self.storage)
+        network.compile()
+        # The simulation should run despite the absence of connections
+        network.run_simulation("test_nest")
+
     def test_brunel(self):
         cfg = get_test_config("brunel")
         simcfg = cfg.simulations.test_nest