황금분할법으로 문제푸는데, 그래프를 그려야 하는 일이 생겼어요

function [x,fx,ea,iter]=goldmax(f,xl,xu,es,maxit,varargin)

if nargin<3,error('at least 3 input arguments required'),end

if nargin<4 || isempty(es), es=0.0001;end

if nargin<5 || isempty(maxit), maxit=50;end

 

phi=(1+sqrt(5))/2;

iter=0;

 

while(1)

    d = (phi-1)*(xu - xl);

    x1 = xl + d;

    x2 = xu - d;

  

    if f(x1,varargin{:}) > f(x2,varargin{:}) 

        xopt = x1;

        xl = x2;

    else

        xopt = x2;

        xu = x1;

    end

    

    iter=iter+1;

   

    if xopt~=0, ea = (2 - phi) * abs((xu - xl) / xopt) * 100;end

    if ea <= es || iter >= maxit,break,end

end

x=xopt;fx=f(xopt,varargin{:});

f=@(x) (-1.5*x.^6-2*x.^4+12*x);

[xopt, fmax, ea, iter]=goldmax(f,0,2,0.0001,3)