function l=b_lineal(x,d,Fx,Gx)
l=1;
alfa=10^(-1);
beta=0.1;
c=1;
 while ((f(x+l*d)>Fx+alfa*l*Gx'*d) || ( gradf(x+l*d)'*d > beta*Gx'*d ))&& c < 100
    l=0.5*l;
    c=c+1;
 end
 end