code: def _rel_err(est_val, true_val):
      return np.abs(est_val - true_val) / np.abs(true_val)
  
imports: from absl.testing import absltest
  from absl.testing import parameterized
  import numpy
  from tensorflow_data_validation.utils import variance_util
label_desc: Use image node_id 3 for calling a global function with example usage: _rel_err(est_val, true_val) and returns: unknown