Matlab-2:二分法工具箱

 function g=dichotomy(f,tol)
 %this routine uses bisection to find a zero of user-supplied
 %continuous function f.the user must supply two points an and bn
 %such that f(an) and f(bn) have different signs .the user also
 %supplies a convergence tolerance delta .
 %this progress is writen by H.D.dong
 % tic;
 % clear
 % clc
 % f=inline('x^3-x^2-1');
 % f=inline('x^6-x-1');
 % f=inline('x^2+1');
 % % h=inline('x^3-x^2-1');
 % % tol=1e-14;
 % % Provides a zero-point presence interval
 % % %
 % % an=1;
 % % bn=2;
 % % %
 % % root=dichotomy(h,tol)
 an=1;
 bn=2;
 root=0;
 if f(an)==0,root=an;bn=root;return;
 elseif f(bn)==0,root=bn;an=root;return;
 elseif sign(f(an))==sign(f(bn)),fprintf('There is no solution in this equation!');
     %%
 %Above showed:there have considered that we have found the root in the first step.
 else
     k=0;
 while (bn-an)>=tol
 midpoint=(bn+an)/2;k=k+1;F(k)=f(midpoint);
     if f(midpoint)==0,root=midpoint;an=root;bn=root;break;
     elseif sign(f(midpoint))~=sign(f(an)),bn=midpoint;
     else
         an=midpoint;
     end
 end
 root=(bn+an)/2;
 end
 g=root;
 % toc;