Lagrange
function lagrange
    x=[-1 0 1];
    y=[10 7 6];

    p=lagint1(x,y)
    polyval(p,x)
    p=lagint2(x,y)
    polyval(p,x)

function p=lagint1(x,y)
    p=zeros(1,length(x));
    t=-1:0.1:1;
    for i=1:length(x)
        pi=deconv(poly(x),poly(x(i)));
        Li=pi/polyval(pi,x(i));
        plot(t,polyval(Li,t),t,y(i)*polyval(Li,t));
        hold on;
        p=p+y(i)*Li;

    end
    plot(t,polyval(p,t));

function p=lagint2(x,y)
    n=length(x);
    X=repmat(x',1,n).^repmat((n-1):-1:0,n,1);   %wandermond mátrix
    p=zeros(1,n);
    for i=1:n;
        temp=X;
        temp(:,i)=y;
        p(i)=det(temp)/det(X);  %wandermond determináns
    end
    hold off;
    t=-1:0.1:1;
    plot(t,polyval(p,t));
    hold on;