code: def x_sum_rows(self, item):
      if self.item_id_to_item[item] in self.meta_dict_item_category:
          alpha = 1
      else:
          print("Error x Sum")
          alpha = 0
  
      sum_g = np.zeros(self.factors)
      for g in self.meta_dict_item_category[self.item_id_to_item[item]]:
          sum_g += self.x[self.g_to_gid[g]]
  
      g_i = len(
          self.meta_dict_item_category[self.item_id_to_item[item]]
      )
      return (sum_g * alpha) / g_i
  
file_path: CaseRecommender/caserec/recommenders/rating_prediction/gsvdplusplus.py
imports: import numpy
  from caserec.recommenders.rating_prediction.matrixfactorization import MatrixFactorization
  from caserec.utils.process_data import ReadFile
label_desc: Use image node_id 7 for calling the GSVDPlusPlus obj's underlying member method code with example usage: obj.x_sum_rows(item) and returns: unknown