diff --git a/Trajectories/cost_function.py b/Trajectories/cost_function.py
index d33c0e6819ecdc66eebb785f531a877aaaa28145..47a22149044a642945fa7bbc0e2b55bc137332d5 100755
--- a/Trajectories/cost_function.py
+++ b/Trajectories/cost_function.py
@@ -55,7 +55,7 @@ def calculate_radii_rossby(properties):
     if n_valid_Rossby != 0: avg_Rossby /= n_valid_Rossby
     return avg_rad, avg_Rossby
 
-def get_slice(array_d_ini, date_index):
+def get_slice(array_d_init, date_index):
     i_slice = bisect.bisect(array_d_init, date_index) - 1
     assert i_slice >= 0
     return i_slice