def _lif_dtcm_usage(size_in, size_out, size_learnt_out, n_neurons,
    n_neurons_in_cluster=None):
    """Approximation of DTCM usage."""
    if n_neurons_in_cluster is None:
        n_neurons_in_cluster = n_neurons
    total_size_out = size_out + size_learnt_out
    size = (n_neurons * (size_in + 3) + total_size_out + 5 * size_in + 
        n_neurons // 2 + n_neurons_in_cluster * total_size_out)
    return size * 4
