How to change a function within a loop at certain point in MATLAB

I have this piece of code:

    x=0:20000;
    
    h0=10;
    alfa0=-0.1*pi/180;
    h=h0+tan(alfa0).*x+10^(-6)*-0.4.*x.^2/(2*(cos(alfa0)^2));
   

Now, when executed it gives me this graph which shows that h is decreasing as x is increasing.

I would like Matlab to stop when h gets to 0, and then use a different function for h. Let's say

 h=2.*x

so we have an actual example.

I tried some stuff with while loops and if statements, but I am getting nowhere. Thanks for the help.

Answer 1

[Stephen23]

" I tried some stuff with while loops and if statements..."

That is entirely the wrong approach in MATLAB. Just use logical indexing:

idx = h<=0;
h(idx) = 2.*x(idx);