code: def _w0(z):
      """Computes the principal branch W_0(z) of the Lambert W function."""
      # Treat -1 / exp(1) separately as special.lambertw() suffers from numerical
      # precision erros exactly at the boundary of z == exp(1)^(-1).
  
      if (
          isinstance(z, float)
          and np.abs(z - (-1.0 / np.exp(1.0))) < 1e-9
      ):
          return -1.0
  
      return np.real(special.lambertw(z, k=0))
  
imports: from absl.testing import parameterized
  import numpy
  from scipy import special
  from scipy import stats
  import tensorflow.compat.v2
  from tensorflow_probability.python.bijectors import lambertw_transform
  from tensorflow_probability.python.internal import test_util
label_desc: Use image node_id 1 for calling a global function with example usage: _w0(z) and returns: np, unknown