Xo = -1;%first x
Xl = 1;%second x
Yo = 0;%first y, y is a function of x
Yl = 0;% second y, y is a function of x

for x = -2:1:2
    P = (Yo*(Xl-x)+(x-Xo)*Yl)/(Xl-Xo)%linear interpolation
    y = 0%actual value
    E = y-P%error
    hold on
    plot(x, E, 'r:+')
end

Xs = 0;%third x
Ys = 0;%third y
for x = -2:1:2
    Lo = (X-Xl)*(X-Xs)/(Xo-Xl)*(Xo-Xs);%L0
    Ll = (X-Xo)*(X-Xs)/(Xl-Xo)*(Xl-Xs);%L1
    Ls = (X-Xo)*(X-Xl)/(Xs-Xo)*(Xs-Xl);%L2
    
    P = Yo*Lo + Yl*Ll + Ys*Ls%quadratic interpolation
    y=0%actual value
    E=y-P%error
end