def additive_self_attention(units, n_hidden=None, n_output_features=None, activation=None):
    """
    Compute additive self attention for time series of vectors (with batch dimension)
            the formula: score(h_i, h_j) = <v, tanh(W_1 h_i + W_2 h_j)>
            v is a learnable vector of n_hidden dimensionality,
            W_1 and W_2 are learnable [n_hidden, n_input_features] matrices

    Args:
        units: tf tensor with dimensionality [batch_size, time_steps, n_input_features]
        n_hidden: number of2784131 units in hidden representation of similarity measure
        n_output_features: number of features in output dense layer
        activation: activation at the output

    Returns:
        output: self attended tensor with dimensionality [batch_size, time_steps, n_output_features]
        """
    n_input_features = K.int_shape(units)[2]
    if n_hidden is None:
        n_hidden = n_input_features
    if n_output_features is None:
        n_output_features = n_input_features
    exp1 = Lambda(lambda x: expand_tile(x, axis=1))(units)
    exp2 = Lambda(lambda x: expand_tile(x, axis=2))(units)
    units_pairs = Concatenate(axis=3)([exp1, exp2])
    query = Dense(n_hidden, activation="tanh")(units_pairs)
    attention = Dense(1, activation=lambda x: softmax(x, axis=2))(query)
    attended_units = Lambda(lambda x: K.sum(attention * x, axis=2))(exp1)
    output = Dense(n_output_features, activation=activation)(attended_units)
    return output
Compute additive self attention for time series of vectors (with batch dimension)
            the formula: score(h_i, h_j) = <v, tanh(W_1 h_i + W_2 h_j)>
            v is a learnable vector of n_hidden dimensionality,
            W_1 and W_2 are learnable [n_hidden, n_input_features] matrices

    Args:
        units: tf tensor with dimensionality [batch_size, time_steps, n_input_features]
        n_hidden: number of2784131 units in hidden representation of similarity measure
        n_output_features: number of features in output dense layer
        activation: activation at the output

    Returns:
        output: self attended tensor with dimensionality [batch_size, time_steps, n_output_features]