def vgg_params(model_name):
    """ Map VGGNet model name to parameter coefficients. """
    params_dict = {'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]
