'Initializes the cell.
Args:
num_units: Number of cell units.
w_initializer: Initializer for the "W" (input) parameter matrices.
u_initializer: Initializer for the "U" (recurrent) parameter matrices.
b_initializer: Initializer for the "b" (bias) parameter vectors.
activation: Cell activation function.'

def __init__(self, num_units, w_initializer, u_initializer, b_initializer, activation=tf.nn.tanh):

    self._num_units = num_units
    self._w_initializer = w_initializer
    self._u_initializer = u_initializer
    self._b_initializer = b_initializer
    self._activation = activation
