Refactor base node creation in RegularNetwork class for improved clar…

…ity and functionality

- Clear previous base nodes before creating new ones to ensure a fresh state.
- Implemented a loop to properly create and assign names to base nodes using smart pointers.
- Enhanced the structure of the FromString method for better readability.

These changes aim to streamline the initialization of base nodes in the contraction tree, improving maintainability and clarity in the network setup process.

src/RegularNetwork.cpp

@@ -536,6 +536,14 @@ namespace cytnx {
 
     this->tensors.resize(this->names.size());
     this->CtTree.base_nodes.resize(this->names.size());
+    this->CtTree.base_nodes.clear();
+
+    // Create base nodes properly
+    for(size_t i = 0; i < this->names.size(); i++) {
+        auto node = std::make_shared<Node>();
+        node->name = this->names[i];
+        this->CtTree.base_nodes.push_back(node);
+    }
 
     // checking if all TN are set in ORDER.
     if (isORDER_exist) {
@@ -640,7 +648,7 @@ namespace cytnx {
       CtTree.build_default_contraction_tree();
     }
     this->einsum_path = CtTree_to_eisumpath(CtTree, names);
-  }
+  } // end of FromString
 
   void RegularNetwork::Fromfile(const string &fname) {
     const cytnx_uint64 MAXLINES = 1024;