Matlab dichotomy to find the optimal solution

No grinding , Look at the code or ：
Here are some .

function [k,y]=erfenfa1(f,a,b,esp)
syms x;
% f Is the function given    a,b  For the given interval ,eps For accuracy 
%  Return value [k,y] Is the horizontal and vertical coordinates of the optimal solution 
while b-a > esp
   % Find out in a,b The derivative of the intermediate point 
    zhong = (b+a)/2;
    dao = subs(diff(f),x,zhong);
    % If the reciprocal is 0, be a,b In the middle zhong  Is the abscissa of the optimal solution 
    if dao == 0
        k=zhong;
        y = subs(f,x,zhong);
        break;
    else 
        % The derivative is less than 0  take zhong Assign a value to a, Greater than 0 Assign to b
        if(dao<0)
            a = zhong;  
        else
            b = zhong;
        end
    end
 % When b-a Less than esp when , take a,b The midpoint is the abscissa of the optimal solution ,y Vertical coordinates 
if b-a<=esp
    k =(b+a)/2;
    y = subs(f,x,k);
end
end

emm… Look at a simple test case ：

>> clear
>> syms x;
f = x^2 + 2*x -1;
[x,y] = erfenfa1(f,-2,0,0.1);
>> [x,y]
 
ans =
 
[ -1, -2]

emm… One more piece ,,, Give me a compliment and I'll show you again , how ..( Manually cheat like )
Bye-bye , Hey .