code: def cfar_alpha(pfa, N):
      """
      Computes the value of alpha corresponding to a given probability
      of false alarm and number of reference cells N.
  
      Parameters
      ----------
      pfa : float
          Probability of false alarm.
  
      N : int
          Number of reference cells.
  
      Returns
      -------
      alpha : float
          Alpha value.
      """
      return N * (pfa ** (-1.0 / N) - 1)
  
imports: from math import ceil, log2
  import cupy
  from ..windows.windows import get_window
label_desc: Use image node_id 4 for calling a global function with example usage: cfar_alpha(pfa, N) and returns: unknown