x=[-5 -4 -3 -2 -1 0 1 2 3 4 5];
y=[0 .254 .508 .762 1.016 1.27 1.016 .762 .508 .254 0];
% Interpolation
xi = linspace(min(x),max(x),100) ;
yi = interp1(x,y,xi) ;
% Fit a quadtratic curve
p = polyfit(xi,yi,2) ;
% plot
plot(x,y,'.r')
hold on
plot(xi,yi,'b')
plot(xi,polyval(p,xi),'k')