code: def _logm_superdiag_entry(l1, l2, t12):
      """
      Compute a superdiagonal entry of a matrix logarithm.
  
      This is like Eq. (11.28) in [1]_, except the determination of whether
      l1 and l2 are sufficiently far apart has been modified.
  
      Parameters
      ----------
      l1 : complex
          A diagonal entry of the matrix.
      l2 : complex
          A diagonal entry of the matrix.
      t12 : complex
          A superdiagonal entry of the matrix.
  
      Returns
      -------
      f12 : complex
          A superdiagonal entry of the matrix logarithm.
  
      Notes
      -----
      Care has been taken to return a real number if possible when
      all of the inputs are real numbers.
  
      References
      ----------
      .. [1] Nicholas J. Higham (2008)
             "Functions of Matrices: Theory and Computation"
             ISBN 978-0-898716-46-7
  
      """
      if l1 == l2:
          f12 = t12 / l1
      elif abs(l2 - l1) > abs(l1 + l2) / 2:
          f12 = t12 * (np.log(l2) - np.log(l1)) / (l2 - l1)
      else:
          z = (l2 - l1) / (l2 + l1)
          u = _unwindk(np.log(l2) - np.log(l1))
          if u:
              f12 = (
                  t12 * 2 * (np.arctanh(z) + np.pi * 1j * u) / (l2 - l1)
              )
          else:
              f12 = t12 * 2 * np.arctanh(z) / (l2 - l1)
      return f12
  
imports: from __future__ import division, print_function, absolute_import
  import warnings
  import numpy
  from scipy.linalg._matfuncs_sqrtm import SqrtmError, _sqrtm_triu
  from scipy.linalg.decomp_schur import schur, rsf2csf
  from scipy.linalg.matfuncs import funm
  from scipy.linalg import svdvals, solve_triangular
  from scipy.sparse.linalg.interface import LinearOperator
  from scipy.sparse.linalg import onenormest
  import scipy.special
label_desc: Use image node_id 5 for calling a global function with example usage: _logm_superdiag_entry(l1, l2, t12) and returns: f12