code: def _convert_to_tridiagonal_format(self, matrix):
      matrix_np = self.evaluate(matrix)
      n = matrix_np.shape[0]
      superdiag = [matrix_np[i, i + 1] for i in range(n - 1)] + [0]
      diag = [matrix_np[i, i] for i in range(n)]
      subdiag = [0] + [matrix_np[i + 1, i] for i in range(n - 1)]
      return tuple(
          tf.constant(v, dtype=matrix.dtype)
          for v in (diag, superdiag, subdiag)
      )
  
file_path: tf-quant-finance/tf_quant_finance/math/pde/steppers/time_marching_schemes_test.py
imports: from absl.testing import parameterized
  import numpy
  import tensorflow.compat.v2
  import tf_quant_finance
  from tensorflow.python.framework import test_util
label_desc: Use image node_id 5 for calling the TimeMarchingSchemeTest obj's underlying member method code with example usage: obj._convert_to_tridiagonal_format(matrix) and returns: tuple