code: def S_white_simple(x):
      """inner covariance matrix for White heteroscedastistity sandwich
  
  
      Parameters
      ----------
      x : ndarray (nobs,) or (nobs, k_var)
          data, for HAC this is array of x_i * u_i
  
      Returns
      -------
      S : ndarray, (k_vars, k_vars)
          inner covariance matrix for sandwich
  
      Notes
      -----
      this is just dot(X.T, X)
  
      """
      if x.ndim == 1:
          x = x[:, None]
  
      return np.dot(x.T, x)
  
imports: import numpy
  from statsmodels.tools.grouputils import combine_indices, group_sums
  from statsmodels.stats.moment_helpers import se_cov
label_desc: Use image node_id 12 for calling a global function with example usage: S_white_simple(x) and returns: np