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Abstract object representing an RNN cell.

Inherits From: Layer

See the Keras RNN API guide for details about the usage of RNN API.

This is the base class for implementing RNN cells with custom behavior.

Every RNNCell must have the properties below and implement call with the signature (output, next_state) = call(input, state).


  class MinimalRNNCell(AbstractRNNCell):

    def __init__(self, units, **kwargs):
      self.units = units
      super(MinimalRNNCell, self).__init__(**kwargs)

    def state_size(self):
      return self.units

    def build(self, input_shape):
      self.kernel = self.add_weight(shape=(input_shape[-1], self.units),
      self.recurrent_kernel = self.add_weight(
          shape=(self.units, self.units),
      self.built = True

    def call(self, inputs, states):
      prev_output = states[0]
      h =, self.kernel)
      output = h +, self.recurrent_kernel)
      return output, output

This definition of cell differs from the definition used in the literature. In the literature, 'cell' refers to an object with a single scalar output. This definition refers to a horizontal array of such units.

An RNN cell, in the most abstract setting, is anything that has a state and performs some operation that takes a matrix of inputs. This operation results in an output matrix with self.output_size columns. If self.state_size is an integer, this operation also results in a new state matrix with self.state_size columns. If self.state_size is a (possibly nested tuple of) TensorShape object(s), then it should return a matching structure of Tensors having shape [batch_size].concatenate(s) for each s in self.batch_size.

output_size Integer or TensorShape: size of outputs produced by this cell.
state_size size(s) of state(s) used by this cell.

It can be represented by an Integer, a TensorShape or a tuple of Integers or TensorShapes.



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