gradient.m

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function G=gradient(str,x)
%  File name:gradient.m      
%  Author:Yan Anxin
%  ID number:081810
%  Date:finished on 2008.11.16
%  Description:  
%       Here defines a function,to get the gradient of the given point    
%       In the syntax G=gradient(str,x),
%       str----input,means the expression of given function
%       x----input,means the given point
%       G=gradient(str,x) returns G, i.e. the gradient of the given point        
             
syms x1 x2
delta=[diff(str,x1);diff(str,x2)];
G=subs(delta,[x1 x2],[x(1) x(2)]);