diff --git a/pypop7/optimizers/core/optimizer.py b/pypop7/optimizers/core/optimizer.py
index 12594d66b..7a408a0f2 100644
--- a/pypop7/optimizers/core/optimizer.py
+++ b/pypop7/optimizers/core/optimizer.py
@@ -57,7 +57,7 @@ def __init__(self, problem, options):
             self.problem_name = self.fitness_function.__name__
 
         # optimizer-related basic options
-        self.options = options
+        self.options = options  # not use `deep copy` to save memory
         self.max_function_evaluations = options.get('max_function_evaluations', np.inf)
         self.max_runtime = options.get('max_runtime', np.inf)
         self.fitness_threshold = options.get('fitness_threshold', -np.inf)