code: def calc_vi_stats(base, perturbed, x_delta):
      """Calculate v_i mean and std.
  
      v_i sensitivity measure following Sobol and Kucherenko (2009)
      For comparison, Morris mu* < sqrt(v_i)
  
      Same as calc_vi_mean but returns standard deviation as well.
      """
      dfdx = ((perturbed - base) / x_delta) ** 2
      return np.mean(dfdx), np.std(dfdx)
  
file_path: SALib/src/SALib/analyze/dgsm.py
imports: from scipy.stats import norm
  import numpy
  from .None import common_args
  from ..util import read_param_file, ResultDict
label_desc: Use image node_id 2 for calling a global function with example usage: calc_vi_stats(base, perturbed, x_delta) and returns: np,  np