code: def flatten_bijector(self):
      n = int((-1 + np.sqrt(1 + 8 * self.dims)) / 2)
      return reshape.Reshape(
          event_shape_in=[n, n], event_shape_out=[n**2]
      )
  
imports: from absl.testing import parameterized
  import numpy
  import tensorflow.compat.v2
  from tensorflow_probability.python.bijectors import exp
  from tensorflow_probability.python.bijectors import reshape
  from tensorflow_probability.python.bijectors import scale
  from tensorflow_probability.python.experimental.tangent_spaces import spaces_test_util
  from tensorflow_probability.python.experimental.tangent_spaces import symmetric_matrix
  from tensorflow_probability.python.internal import test_util
  from tensorflow_probability.python.math import linalg
label_desc: Use image node_id 5 for calling the _SymmetricMatrixTest obj's underlying member method code with example usage: obj.flatten_bijector() and returns: reshape