function y = mean(x,dim)  %函數定義行，注意函數名稱必須與文件名稱相同
%MEAN   Average or mean value.——H1幫助行
%   For vectors, MEAN(X) is the mean value of the elements in X. For
%   matrices, MEAN(X) is a row vector containing the mean value of
%   each column.  For N-D arrays, MEAN(X) is the mean value of the
%   elements along the first non-singleton dimension of X.——函數體說明
%
%   MEAN(X,DIM) takes the mean along the dimension DIM of X. 
%
%   Example: If X = [0 1 2
%                    3 4 5]
%
%   then mean(X,1) is [1.5 2.5 3.5] and mean(X,2) is [1
%                                                     4]
%
%   See also MEDIAN, STD, MIN, MAX, COV.

%   Copyright (c) 1984-98 by The MathWorks, Inc.
%   $Revision: 5.13 $  $Date: 1997/11/21 23:23:55 $——注解

%函數主體
if nargin==1, %nargin指函數的輸入變量數；nargout指函數的輸出變量數
  % Determine which dimension SUM will use
  dim = min(find(size(x)~=1));%size 求矩陣的行數與列數，find找出非零元素的索引號
  if isempty(dim), dim = 1; end

  y = sum(x)/size(x,dim);
else
  y = sum(x,dim)/size(x,dim);
end