// Lignes de niveau


deff('[z]=myphi(x,y)','z=(x.^2)/2+(y.^2).*cos(x)');
x=-5:0.1:5;
y=x;
[m n]=size(x);
z=zeros(n,n);
for i=1:n
    for j=1:n
        z(i,j)=myphi(x(i),y(j));
    end
end

clf();
colorbar(min(z),max(z));
Sgrayplot(x,y,z);
title('Lignes de niveau de phi');

//pause;

// Gradient à pas fixe

deff('[Y]=mygradphi(X)','Y=[X(1).^2-X(2)*sin(X(1)),2*X(2).*cos(X(1))]');

rho=0.9;
    X=[1,1];
    Y=X;
 for i=1:19
    Y=Y-rho*mygradphi(Y);
    X=[X;Y];
 end

rho=1.1;
    Xbis=[1,1];
    Ybis=Xbis;
 for i=1:19
    Ybis=Ybis-rho*mygradphi(Ybis);
    Xbis=[Xbis;Ybis];
 end
 
 plot(X(:,1),X(:,2),'ro',Xbis(:,1),Xbis(:,2),'b*');
 legend('moins','plus');