How to limit data from a fit?

I have a custom fit that fits data that I've plotted. I now want to try to limit the range in which the fit occurs. I want it to limit where x is less than 150.

Here is my current code:

rho=Resistivityohmcm;
T=TemperatureK;

plot(T,rho,'-o')

x=T;
y=rho;

fnPolySq=@(p1,p2,x) p1*x.^2 + p2;
fit(x,y,fnPolySq)

plot(f,T,rho)
disp (f)

Answer 1

[Walter Roberson]

mask = x < 150;
f = fit(x(mask), y(mask), fnPolySq);
plot(f, T, rho)

Answer 2

[Aquatris]

Create new variables;

range = find(x<150);
xNew = x(range)
yNew = y(range)

Obtain your fit using xNew and yNew variables instead of x and y.