function X = diff(X,order,dim)
%1.數值差分
%     對向量n維X,diff(X)返回[X(2)-X(1)  X(3)-X(2) ... X(n)-X(n-1)]
%  例     x=[1 3 8];diff(x)
%
%2.符號導函數
%    diff(s)符號表達式s的導數.  
%    diff(s,v)符號表達式s關于變量v的導數.
%    diff(s,n)符號表達式s的n階導數.
%    diff(s,v,n),符號表達式s關于變量v的n階導數.
% 例     syms x y;
%       s=exp(x^2)*sin(x+y);
%       diff(s,x,2)
%
%DIFF Difference and approximate derivative.
%   DIFF(X), for a vector X, is [X(2)-X(1)  X(3)-X(2) ... X(n)-X(n-1)].
%   DIFF(X), for a matrix X, is the matrix of column differences,
%      [X(2:n,:) - X(1:n-1,:)].
%   DIFF(X), for an N-D array X, is the difference along the first
%      non-singleton dimension of X.
%   DIFF(X,N) is the N-th order difference along the first non-singleton 
%      dimension (denote it by DIM). If N >= size(X,DIM), DIFF takes 
%      successive differences along the next non-singleton dimension.
%   DIFF(X,N,DIM) is the Nth difference function along dimension DIM. 
%      If N >= size(X,DIM), DIFF returns an empty array.
%
%   Examples:
%      h = .001; x = 0:h:pi;
%      diff(sin(x.^2))/h is an approximation to 2*cos(x.^2).*x
%      diff((1:10).^2) is 3:2:19
%
%      If X = [3 7 5
%              0 9 2]
%      then diff(X,1,1) is [-3 2 -3], diff(X,1,2) is [4 -2
%                                                     9 -7],
%      diff(X,2,2) is the 2nd order difference along the dimension 2, and
%      diff(X,3,2) is the empty matrix.
%
%   See also GRADIENT, SUM, PROD.

%   Copyright (c) 1984-98 by The MathWorks, Inc.
%   $Revision: 5.20 $  $Date: 1997/11/21 23:23:41 $
%   Built-in function.