diff --git a/abcvoting/abcrules_gurobi.py b/abcvoting/abcrules_gurobi.py
index 709a4f6..4abf087 100644
--- a/abcvoting/abcrules_gurobi.py
+++ b/abcvoting/abcrules_gurobi.py
@@ -169,7 +169,7 @@ def set_opt_model_func(model, in_committee):
                 utility[(voter, x)] = model.addVar(vtype=gb.GRB.BINARY, name=f"utility({i,x})")
 
         # constraint: the committee has the required size
-        model.addConstr(gb.quicksum(in_committee) == committeesize)
+        model.addConstr(in_committee.sum() == committeesize)
 
         # constraint: utilities are consistent with actual committee
         for voter in profile:
@@ -234,7 +234,7 @@ def set_opt_model_func(model, in_committee):
                 utility[(voter, x)] = model.addVar(vtype=gb.GRB.BINARY, name=f"utility({i, x})")
 
         # constraint: the committee has the required size
-        model.addConstr(gb.quicksum(in_committee) == committeesize)
+        model.addConstr(in_committee.sum() == committeesize)
 
         # constraint: utilities are consistent with actual committee
         for voter in profile:
@@ -663,7 +663,7 @@ def set_opt_model_func(model, in_committee):
                     voteratmostdistances[(i, dist)] = 0
 
         # constraint: the committee has the required size
-        model.addConstr(gb.quicksum(in_committee) == committeesize)
+        model.addConstr(in_committee.sum() == committeesize)
 
         # constraint: distances are consistent with actual committee
         for i, voter in enumerate(profile):
diff --git a/abcvoting/properties.py b/abcvoting/properties.py
index 6f36332..f644a6b 100644
--- a/abcvoting/properties.py
+++ b/abcvoting/properties.py
@@ -662,7 +662,7 @@ def _check_pareto_optimality_gurobi(profile, committee):
 
     # constraint: the condition of having strictly more approved candidates in
     # dominating committee will be satisfied for at least one voter
-    model.addConstr(gb.quicksum(condition_strictly_more) >= 1)
+    model.addConstr(condition_strictly_more.sum() >= 1)
 
     # constraint: all voters should have at least as many preferred candidates
     # in the dominating committee as in the query committee.
@@ -675,7 +675,7 @@ def _check_pareto_optimality_gurobi(profile, committee):
         )
 
     # constraint: committee has the right size
-    model.addConstr(gb.quicksum(in_committee) == len(committee))
+    model.addConstr(in_committee.sum() == len(committee))
 
     # set the objective function
     model.setObjective(
@@ -816,7 +816,7 @@ def _check_EJR_gurobi(profile, committee, quota):
     in_cut = model.addVars(profile.num_cand, vtype=gb.GRB.BINARY, name="in_cut")
 
     # the voters in group should agree on at least ell candidates
-    model.addConstr(gb.quicksum(in_cut) >= ell)
+    model.addConstr(in_cut.sum() >= ell)
 
     # candidates in cut should be approved by all voters in group
     for vi, voter in enumerate(profile):
@@ -968,7 +968,7 @@ def _check_PJR_gurobi(profile, committee, quota):
     in_cut = model.addVars(profile.num_cand, vtype=gb.GRB.BINARY, name="in_cut")
 
     # the voters in group should agree on at least ell candidates
-    model.addConstr(gb.quicksum(in_cut) >= ell)
+    model.addConstr(in_cut.sum() >= ell)
 
     # candidates in cut should be approved by all voters in group
     for vi, voter in enumerate(profile):
@@ -1521,10 +1521,10 @@ def _check_FJR_gurobi(profile, committee, quota):
 
     # coalition large enough to deserve |set_of_candidates| seats
     model.addConstr(
-        gb.quicksum(set_of_candidates) * quota
+        set_of_candidates.sum() * quota
         <= gb.quicksum(voter.weight * set_of_voters[vi] for vi, voter in enumerate(profile))
     )
-    model.addConstr(gb.quicksum(set_of_voters) >= 1)
+    model.addConstr(set_of_voters.sum() >= 1)
     for i, voter in enumerate(profile):
         # if i is in set_of_voters, then:
         # (a) i has utility at most beta-1 in committee
@@ -1703,10 +1703,10 @@ def _check_core_gurobi(profile, committee, quota):
 
     # set_of_voters is large enough to afford set_of_candidates
     model.addConstr(
-        gb.quicksum(set_of_candidates) * quota
+        set_of_candidates.sum() * quota
         <= gb.quicksum(voter.weight * set_of_voters[vi] for vi, voter in enumerate(profile))
     )
-    model.addConstr(gb.quicksum(set_of_voters) >= 1)
+    model.addConstr(set_of_voters.sum() >= 1)
 
     # every voter in set_of_voters prefers set_of_candidates to committee
     for i, voter in enumerate(profile):
diff --git a/examples/preflib-files/new_example.cat b/examples/preflib-files/new_example.cat
index 9dac5ba..70ac817 100644
--- a/examples/preflib-files/new_example.cat
+++ b/examples/preflib-files/new_example.cat
@@ -1,4 +1,4 @@
-# FILE NAME: new_example.cat
+# FILE NAME: /home/martin/Documents/code/pycharm-projects/abcvoting/examples/preflib-files/new_example.cat
 # TITLE: 
 # DESCRIPTION: 
 # DATA TYPE: 
diff --git a/tests/data/test5.cat b/tests/data/test5.cat
index 8717f42..1adf044 100644
--- a/tests/data/test5.cat
+++ b/tests/data/test5.cat
@@ -1,4 +1,4 @@
-# FILE NAME: test5.cat
+# FILE NAME: /home/martin/Documents/code/pycharm-projects/abcvoting/tests/data/test5.cat
 # TITLE: 
 # DESCRIPTION: 
 # DATA TYPE: