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: Judgment.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 s=Judgment(f,str)
%JUDGMENT   判断函数的单调性或凹凸性
% S=JUDGMENT(F,STR)

    
function s=Judgment(f,str)
%JUDGMENT   判断函数的单调性或凹凸性
% S=JUDGMENT(F,STR)
%
% 输入参数：
%     ---F：实数
%     ---STR：性质类型字符串元胞数组
% 输出参数：
%     ---S：返回的性质类型字符串
%
% See also iscellstr, cellstr

if ~iscellstr(str) || numel(str)~=2
    error('Input argument str is Illegal.')
end