function t4=insert(x0,p0)
syms t;
count=0;
p0=[2 0];
x0=[0 0];
[phai g]=simple(myfun(x0+t*(p0)));
%phai=(t+1)*(t-2)^2;
[a b c]=searchstep(phai);
sigma=0.00001;
t1=a;
t2=b;
t3=c;
phai1=subs(phai,t1);
phai2=subs(phai,t2);
phai3=subs(phai,t3);
t4=((t2^2-t3^2)*phai1+(t3^2-t1^2)*phai2+(t1^2-t2^2)*phai3)/(2*((t2-t3)*phai1+(t3-t1)*phai2+(t1-t2)*phai3));
phai4=subs(phai,t4);
%abs(phai2-phai4)
while abs(phai2-phai4)>sigma
     if t4>t2
        if (phai2>=phai4)&(phai4<=phai3)
            t1=t2;
            t2=t4;
            phai1=phai2;
            phai2=phai4;
        else
            t3=t4;
            phai3=phai4;
        end
    else
        if (phai1>=phai4)&(phai4<=phai2)
            t3=t2;
            t2=t4;
            phai3=phai2;
            phai2=phai4;
        else
            t1=t4;
            phai1=phai4;
        end
    end
    t4=((t2^2-t3^2)*phai1+(t3^2-t1^2)*phai2+(t1^2-t2^2)*phai3)/(2*((t2-t3)*phai1+(t3-t1)*phai2+(t1-t2)*phai3))
    phai4=subs(phai,t4)
    count=count+1
end