def plot_transforms(ace_model, fname='ace_transforms.png'):
    """Plot the transforms."""
    if not plt:
        raise ImportError('Cannot plot without the matplotlib package')
    plt.rcParams.update({'font.size': 8})
    plt.figure()
    num_cols = len(ace_model.x) / 2 + 1
    for i in range(len(ace_model.x)):
        plt.subplot(num_cols, 2, i + 1)
        plt.plot(ace_model.x[i], ace_model.x_transforms[i], '.', label='Phi {0}'.format(i))
        plt.xlabel('x{0}'.format(i))
        plt.ylabel('phi{0}'.format(i))
    plt.subplot(num_cols, 2, i + 2)  # pylint: disable=undefined-loop-variable
    plt.plot(ace_model.y, ace_model.y_transform, '.', label='Theta')
    plt.xlabel('y')
    plt.ylabel('theta')
    plt.tight_layout()

    if fname:
        plt.savefig(fname)
        return None
    return plt
Plot the transforms.