opt5.py

class AddSign(optimizer.Optimizer):
    """Implementation of AddSign.
    See [Bello et. al., 2017](https://arxiv.org/abs/1709.07417)
    @@__init__
    """

    def __init__(self, learning_rate=1.001,alpha=0.01,beta=0.5, use_locking=False, name="AddSign"):
        super(AddSign, self).__init__(use_locking, name)
        self._lr = learning_rate
        self._alpha = alpha
        self._beta = beta
        
        # Tensor versions of the constructor arguments, created in _prepare().
        self._lr_t = None
        self._alpha_t = None
        self._beta_t = None
      
    def _prepare(self):
        self._lr_t = ops.convert_to_tensor(self._lr, name="learning_rate")
        self._alpha_t = ops.convert_to_tensor(self._beta, name="beta_t")
        self._beta_t = ops.convert_to_tensor(self._beta, name="beta_t")

    def _create_slots(self, var_list):
        # Create slots for the first and second moments.
        for v in var_list:
            self._zeros_slot(v, "m", self._name)

    def _apply_dense(self, grad, var):
        lr_t = math_ops.cast(self._lr_t, var.dtype.base_dtype)
        beta_t = math_ops.cast(self._beta_t, var.dtype.base_dtype)
        alpha_t = math_ops.cast(self._alpha_t, var.dtype.base_dtype)
    
        eps = 1e-7 #cap for moving average
        
        m = self.get_slot(var, "m")
        m_t = m.assign(tf.maximum(beta_t * m + eps, tf.abs(grad)))
        
        var_update = state_ops.assign_sub(var, lr_t*grad*(1.0+alpha_t*tf.sign(grad)*tf.sign(m_t) ) )
        #Create an op that groups multiple operations
        #When this op finishes, all ops in input have finished
        return control_flow_ops.group(*[var_update, m_t])

    def _apply_sparse(self, grad, var):
        raise NotImplementedError("Sparse gradient updates are not supported.")