local search

src/local_search.py

@@ -5,7 +5,6 @@ else:
     from AI2019.src.utils import *
 
 
-
 class TwoOpt:
 
     @staticmethod
@@ -67,3 +66,84 @@ class TwoOpt:
 
         return new_tsp_sequence.tolist(), new_len, uncross
 
+
+class TwoDotFiveOpt:
+
+  @staticmethod
+  def step2dot5opt(solution, matrix_dist, distance):
+      """
+      One step of 2opt, one double loop and return first improved sequence
+      @param tsp_sequence:
+      @param matrix_dist:
+      @param distance:
+      @return:
+      """
+      seq_length = len(solution) - 2
+      tsp_sequence = np.array(solution)
+      uncrosses = 0
+      for i in range(1, seq_length - 1):
+          for j in range(i + 1, seq_length):
+            # 2opt swap
+            twoOpt_tsp_sequence = TwoOpt.swap2opt(tsp_sequence, i, j)
+            twoOpt_len = distance + TwoOpt.gain(i, j , tsp_sequence, matrix_dist)
+            # node shift 1
+            first_shift_tsp_sequence = TwoDotFiveOpt.shift1(tsp_sequence, i,j)
+            first_shift_len = distance + TwoDotFiveOpt.shift_gain1(i,j, tsp_sequence, matrix_dist)
+            # node shift 2
+            second_shift_tsp_sequence = TwoDotFiveOpt.shift2(tsp_sequence, i,j)
+            second_shift_len = distance + TwoDotFiveOpt.shift_gain2(i,j, tsp_sequence, matrix_dist)
+
+            best_len, best_method = min([twoOpt_len, first_shift_len, second_shift_len]), np.argmin([twoOpt_len, first_shift_len, second_shift_len])
+            sequences = [twoOpt_tsp_sequence, first_shift_tsp_sequence, second_shift_tsp_sequence]
+            if best_len < distance:
+              uncrosses += 1
+              tsp_sequence = sequences[best_method]
+              distance = best_len
+              # print(distance, best_method, [twoOpt_len, first_shift_len, second_shift_len])
+      return tsp_sequence, distance, uncrosses
+
+  @staticmethod
+  def shift1(tsp_sequence, i, j):
+    new_tsp_sequence = np.concatenate([tsp_sequence[:i], tsp_sequence[i+1: j+1], [tsp_sequence[i]], tsp_sequence[j+1:]])
+    return new_tsp_sequence
+
+  @staticmethod
+  def shift_gain1(i, j , tsp_sequence, matrix_dist):
+    old_link_len = (matrix_dist[tsp_sequence[i], tsp_sequence[i - 1]]+ matrix_dist[tsp_sequence[i], tsp_sequence[i + 1]] + matrix_dist[tsp_sequence[j], tsp_sequence[j + 1]])
+    changed_links_len = (matrix_dist[tsp_sequence[i - 1], tsp_sequence[i + 1]] + matrix_dist[tsp_sequence[i], tsp_sequence[j]] + matrix_dist[tsp_sequence[i], tsp_sequence[j + 1]])
+    return - old_link_len + changed_links_len
+
+  @staticmethod
+  def shift2(tsp_sequence, i, j):
+    new_tsp_sequence = np.concatenate([tsp_sequence[:i], [tsp_sequence[j]], tsp_sequence[i: j], tsp_sequence[j+1:]])
+    return new_tsp_sequence
+
+  @staticmethod
+  def shift_gain2(i, j , tsp_sequence, matrix_dist):
+    old_link_len = (matrix_dist[tsp_sequence[i], tsp_sequence[i - 1]] + matrix_dist[tsp_sequence[j], tsp_sequence[j - 1]] + matrix_dist[tsp_sequence[j], tsp_sequence[j + 1]])
+    changed_links_len = (matrix_dist[tsp_sequence[j], tsp_sequence[i - 1]] + matrix_dist[tsp_sequence[i], tsp_sequence[j]] + matrix_dist[tsp_sequence[j - 1], tsp_sequence[j + 1]])
+    return - old_link_len + changed_links_len
+
+  @staticmethod
+  def loop2dot5opt(solution, instance, max_num_of_changes=400):  # Iterate stoep2opt max_iter times (2-opt local search)
+      """
+
+      @param tsp_sequence:
+      @param instance:
+      @param max_num_of_changes:
+      @return:
+      """
+      matrix_dist = instance.dist_matrix
+      actual_len = compute_lenght(solution, matrix_dist)
+      new_tsp_sequence = np.copy(np.array(solution))
+      uncross = 0
+      while uncross < max_num_of_changes:
+          new_tsp_sequence, new_len, uncr_ = TwoDotFiveOpt.step2dot5opt(new_tsp_sequence, matrix_dist, actual_len)
+          uncross += uncr_
+          # print(new_len, uncross)
+          if new_len < actual_len:
+              actual_len = new_len
+          else:
+              return new_tsp_sequence.tolist(), actual_len, uncross
+      return new_tsp_sequence.tolist(), actual_len, uncross
+