# Least Common Multiple

1. Jan 6, 2013

### pyroknife

I'm reading this programming code that basically says if 1 of 2 variables (x and y) is less than 0, then their least common multiple is 0.

If we have x=-2 and y=+3, then their least common multiple is 0.

I don't get it. I know what a least common multiple is, but this one isn't very intuitive to me.

Can someone explain?

2. Jan 6, 2013

### lurflurf

That is not the usual definition. Usually lcm(-2,3)=6 and
lcm(a,b)=|ab|/gcd(a,b)

3. Jan 6, 2013

### micromass

Well, it's just a definition. It's not the usual definition and it's probably not a very useful one either. So there is no explanation other that the authors of the code implemented things like this.

4. Jan 6, 2013

### pyroknife

Part of the code written in C is:
if ( u < 0 || v < 0 )
return 0;

The overall code asks to find the lcm of u and v. If u or v is <0, then lcm of u and v is 0.

5. Jan 6, 2013

### haruspex

Looks like the author considered it an error case and used a result of zero to signal an error condition back to the caller. This ought to be part of the declared interface. (But what does it return if an operand is 0?)
If negative values are valid in your case, just wrap the operands in abs().