code: def _bessel_iv_ratio_bwd(aux, g):
      """Reverse mode impl for bessel_iv_ratio."""
      v, z = aux
      pz = _bessel_iv_ratio_partial(v, z)
      grad_z = pz * g
      _, grad_z = tfp_math.fix_gradient_for_broadcasting(
          [v, z], [tf.ones_like(grad_z), grad_z]
      )
      return None, grad_z
  
imports: import numpy
  import tensorflow.compat.v2
  from tensorflow_probability.python.internal import custom_gradient
  from tensorflow_probability.python.internal import dtype_util
  from tensorflow_probability.python.internal import prefer_static
  from tensorflow_probability.python.math import generic
label_desc: Use image node_id 6 for calling a global function with example usage: _bessel_iv_ratio_bwd(aux, g) and returns: None,  grad_z