How to implement this particular rect function?

Now I know this will sound dumb, but I am failing to understand this implementation

So I have the logic here,

if f(x)=rect(2x) is the question; 

 x=-lower limit : increment : upper limit;
 y=abs(x) <= 1;
 y = y * amplitude;

This is the simplest code there is to implement it.

Now, the problem is, I have to implement f(x)=rect(|x|/a)
where|x| = hypot(x1,x2) which is gonna be iterating every for loop.

I am however confused how to implement this in the above example.

Please help.

Thanks, Rohan