bisect.m
function [x_star,index,num]=bisect(fun,a,b,ep)
fa=feval(fun,a);
fb=feval(fun,b);
if fa*fb>0 
x_star=[fa,fb];
index=0;
mum=0;
return;
end
k=1;




while(abs(b-a)/2)>=ep
    x=(a+b)/2;
    fx=feval(fun,x);
    if fa*fx<0
        b=x;
        fb=fx;
    else
        a=x;
        fa=fx;
    end
    k=k+1;
end
x_star=(a+b)/2;
index=1;
num=k;