You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: Evolute_Draw.m
    path of file: ./repos/Algorithms_MathModels/《基于MATLAB的高等数学问题求解》 随书附带源程序/CH07
    
    the code of the file until where you have to start completion: function Evolute_Draw(varargin)
%EVOLUTE_DRAW   绘制曲线的渐屈线
% EVOLUTE_DRAW(FUN,RANGE)
% EVOLUTE_DRAW(FUNX,FUNY,RANGE)
%
% 输入参数：
%     ---FUN：曲线函数的一般方程
%     ---FUNX,FUNY：曲线函数的参数方程
%     ---RANGE：绘图区间
%

    
function Evolute_Draw(varargin)
%EVOLUTE_DRAW   绘制曲线的渐屈线
% EVOLUTE_DRAW(FUN,RANGE)
% EVOLUTE_DRAW(FUNX,FUNY,RANGE)
%
% 输入参数：
%     ---FUN：曲线函数的一般方程
%     ---FUNX,FUNY：曲线函数的参数方程
%     ---RANGE：绘图区间
%
% See also diff, diff_para

args=varargin;
range=args{end};
if nargin==2
    y=args{1};
    x=sym('x','real');
    s=symvar(y);
    if length(s)>1
        error('函数fun必须只包含一个符号变量.')
    end