function pk=Cauchy_point(radius_k,df,Bk,Xk)

pt2=Xk(1,1);
pt3=Xk(2,1);
pr2=Xk(3,1);
pr3=Xk(4,1);


gk=eval(df);

if gk.'*Bk*gk<=0
    tao_k=1;
else tao_k=min((norm(gk))^3/(radius_k*gk.'*Bk*gk),1);
end

pk=-tao_k*radius_k/(norm(gk))*gk;


