How to set x > 0, at 2nd order polynomial using polyfit.

Hi I need help, I have imported a txt file into my matlab and have set the x and y value, then I got stuck to create the line on graph at x > 0. Below is my normal code without set x > 0.

p2 = polyfit(x,y,2);
f = polyval(p2,x);
plot(x,f,'-')  

Answer 1

[KSSV]

idx = x > 0 ; 
x = x(idx);
y = y(idx) ; 

p2 = polyfit(x,y,2);
f = polyval(p2,x);
plot(x,f,'-')  

[Nurul Hazira]

it is working now! thank you so much :)