Non-Dominant Sorting for NSGA-II

Author: ahmedfgad

NSGA-II/non_dominant_sorting.py

@@ -0,0 +1,62 @@
+import numpy
+
+population = numpy.array([[20, 2.2],
+                          [60, 4.4],
+                          [65, 3.5],
+                          [15, 4.4],
+                          [55, 4.5],
+                          [50, 1.8],
+                          [80, 4.0],
+                          [25, 4.6]])
+
+def non_dominant_sorting(curr_set):
+    # List of the members of the current dominant front/set.
+    dominant_set = []
+    # List of the non-members of the current dominant front/set.
+    non_dominant_set = []
+    for idx1, sol1 in enumerate(curr_set):
+        # Flag indicates whether the solution is a member of the current dominant set.
+        is_dominant = True
+        for idx2, sol2 in enumerate(curr_set):
+            if idx1 == idx2:
+                continue
+            # Zipping the 2 solutions so the corresponding genes are in the same list.
+            # The returned array is of size (N, 2) where N is the number of genes.
+            b = numpy.array(list(zip(sol1, sol2)))
+    
+            #TODO Consider repacing < by > for maximization problems.
+            # Checking for if any solution dominates the current solution by applying the 2 conditions.
+            # le_eq: All elements must be True.
+            # le: Only 1 element must be True.
+            le_eq = b[:, 1] <= b[:, 0]
+            le = b[:, 1] < b[:, 0]
+
+            # If the 2 conditions hold, then a solution dominates the current solution.
+            # The current solution is not considered a member of the dominant set.
+            if le_eq.all() and le.any():
+                # print(f"{sol2} dominates {sol1}")
+                # Set the is_dominant flag to False to not insert the current solution in the current dominant set.
+                # Instead, insert it into the non-dominant set.
+                is_dominant = False
+                non_dominant_set.append(sol1)
+                break
+            else:
+                # Reaching here means the solution does not dominant the current solution.
+                # print(f"{sol2} does not dominate {sol1}")
+                pass
+
+        # If the flag is True, then no solution dominates the current solution.
+        if is_dominant:
+            dominant_set.append(sol1)
+
+    # Return the dominant and non-dominant sets.
+    return dominant_set, non_dominant_set
+
+dominant_set = []
+non_dominant_set = population.copy()
+while len(non_dominant_set) > 0:
+    d1, non_dominant_set = non_dominant_sorting(non_dominant_set)
+    dominant_set.append(d1)
+
+for i, s in enumerate(dominant_set):
+    print(f'Dominant Front Set {i+1}:\n{s}')