function X = diff(X,order,dim)
%1.数值差分
% 对向量n维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.符号导函数
% diff(s)符号表达式s的导数.
% diff(s,v)符号表达式s关于变量v的导数.
% diff(s,n)符号表达式s的n阶导数.
% diff(s,v,n),符号表达式s关于变量v的n阶导数.
% 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.
