def define_logistic_regression(n_classes, l1_reg=0, l2_reg=0):
    """Shortcut to build the list of layer definitions (a single layer,
    in this case) for a logistic regression classifier.

    Parameters
    ----------
    n_classes : int
        Number of classes to calculate probabilities for
    l1_reg, l2_reg : float, optional
        L1 and L2 regularization strengths

    Returns
    -------
    list
        Layer definitions suitable for input to a `NNClassifier`
    """
    # This network is only an output layer.
    layer_defs = [["ClassificationOutputLayer", {"n_classes": n_classes,
                                                 "l1": l1_reg, "l2": l2_reg}]]
    return layer_defs