types.
*   Math and Linear Algebra:
    *   Add `tf.linalg.LinearOperatorTridiag`.
    *   Add `LinearOperatorBlockLowerTriangular`
    *   Add broadcasting support to
        tf.linalg.triangular_solve[#26204](https://github.com/tensorflow/tensorflow/issues/26204),
        tf.math.invert_permutation.
    *   Add `tf.math.sobol_sample` op.
    *   Add `tf.math.xlog1py`.