message: Explicitly pointing out that tf.sparse.SparseTensors are not supported.
diff: @@ -2880,8 +2880,16 @@ def matmul(a,
  multiplication.
  adjoint_b: If `True`, `b` is conjugated and transposed before
  multiplication.
  - a_is_sparse: If `True`, `a` is treated as a sparse matrix.
  - b_is_sparse: If `True`, `b` is treated as a sparse matrix.
  + a_is_sparse: If `True`, `a` is treated as a sparse matrix. Notice, this
  + **does not support `tf.sparse.SparseTensor`**, it just makes optimizations
  + that assume most values in `a` are zero.
  + See `tf.sparse.sparse_dense_matmul`
  + for some support for `tf.SparseTensor` multiplication.
  + b_is_sparse: If `True`, `b` is treated as a sparse matrix. Notice, this
  + **does not support `tf.sparse.SparseTensor`**, it just makes optimizations
  + that assume most values in `a` are zero.
  + See `tf.sparse.sparse_dense_matmul`
  + for some support for `tf.SparseTensor` multiplication.
  name: Name for the operation (optional).
  Returns:
  