def vggnet_params(model_name):
    """ Map VGGNet model name to parameter coefficients. """
    params_dict = {
        # Coefficients: cfg, res, batch_norm
        "vgg11":    ("A", 224, False),
        "vgg13":    ("B", 224, False),
        "vgg16":    ("D", 224, False),
        "vgg19":    ("E", 224, False),
        "vgg11_bn": ("A", 224, True),
        "vgg13_bn": ("B", 224, True),
        "vgg16_bn": ("D", 224, True),
        "vgg19_bn": ("E", 224, True),
    }
    return params_dict[model_name]