function pf_eval(Np)
N = 100;
kn = 0.05;
R = 4;
x = (0:N-1)/N;
xr = x(1:R:N)
y = sin(0.25*2*pi*xr);

Nr = length(xr);
yn = y + kn*(0.5-rand(1,Nr));
[p,s] = myPolyfit(xr,yn,Np);

yh = polyval(p,x);

plot(xr, yn, 'ro', x, yh, 'b.'); grid; legend('y','y_h');
s=s