Fix MIP toggle bug: handle PuLP import gracefully

mip.py

@@ -3,7 +3,12 @@ import pandas as pd
 from scipy.spatial import distance_matrix
 from scipy.sparse.csgraph import minimum_spanning_tree
 from collections import defaultdict
-import pulp
+import random
+
+try:
+    import pulp
+except ImportError:
+    pulp = None
 
 
 def design_with_mip(
@@ -32,14 +37,20 @@ def design_with_mip(
     :param get_max_capacity_func: 获取最大容量函数
     :return: 连接列表和带有簇信息的turbines
     """
+    if pulp is None:
+        print(
+            "WARNING: PuLP library not available. MIP optimization skipped, falling back to MST."
+        )
+        from main import design_with_mst
+
+        return design_with_mst(turbines, substation)
+
     if get_max_capacity_func:
         max_mw = get_max_capacity_func(cable_specs, voltage, power_factor)
     else:
         max_mw = 100.0  # 默认值
-
     total_power = turbines["power"].sum()
-    if max_clusters is None:
-        max_clusters = int(np.ceil(total_power / max_mw))
+    max_clusters = int(np.ceil(total_power / max_mw))
     n_turbines = len(turbines)
 
     # 预计算距离矩阵