code: def std2(X, X_mean):
      """Numba standard deviation function for a 1d numpy array with pre-calculated mean.
  
      Parameters
      ----------
      X : 1d numpy array
          A 1d numpy array of values
      X_mean : float
          The mean of the input array
  
      Returns
      -------
      std : float
          The standard deviation of the input array
      """
      s = 0
      for i in range(X.shape[0]):
          s += (X[i] - X_mean) ** 2
      return (s / X.shape[0]) ** 0.5
  
imports: from sktime.utils.validation._dependencies import _check_soft_dependencies
  import numpy
  import sktime.utils.numba.general
  from sktime.utils.numba.njit import njit
label_desc: Use image node_id 10 for calling a global function with example usage: std2(X, X_mean) and returns: unknown