function gradient2d()
%%%%%%%%%%%%%%
x(1)=-1.5
x(2)=1.5
t=0.0001
kmax=10000
for i=1:kmax;
    d=-g(x);
    x=x+t*d
    abs_grad_f=norm(g(x))
    f_val=f(x)
    y(i,:)=x;
end
%%%%%%%%%%%%%%%%%
%%% Partie Plot
%%%%%%%%%%%%%%%%%
x1 = -3:0.1:3;
x2= -3:0.1:3;
[x1,x2] = meshgrid(x1,x2);
Z = 100*(x2-x1.^2).^2 + (1-x2).^2;
contourf(x1,x2,Z,10);
hold on
plot(y(:,1),y(:,2),'w.')
colormap jet
%%%%%%%%%%%%%%%%%
function d=f(x);
% d = (x(1)-1).^2+(x(2)-1).^2;
 d=100*(x(2)-x(1).^2).^2 + (1-x(1)).^2;
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 function d=g(x);
 %d(1) = 2*(x(1)-1);%d(2) = 2*(x(2)-1);
 d(1)=-(400*(x(2)-x(1).^2)).*x(1)-2+2*x(1);
 d(2)=200*x(2)-200*x(1).^2;
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 function y=thetap(t,x,d);
 y=g(x+t*d)*d';
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 %%%Recherche lineaire
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 function tk=RL(t,x,d);
    kmax=100
    alpha=1.2
    beta=0.9
    for i=1:kmax;
        if (thetap(t)<0)
            t=alpha*t            
        elseif (thetap(t)>0)
            t=beta*t
        end
end