# [racket-dev] feature request: gcd, lcm for rationals

On 12/9/11 3:31 PM, Daniel King wrote:
>* On Fri, Dec 9, 2011 at 15:27, Carl Eastlund<cce at ccs.neu.edu> wrote:
*>>* What does "divides" even mean in Q? I think we need David to explain
*>>* what his extension of GCD and LCM means here, in that "divisors" and
*>>* "multiples" are fairly trivial things in Q.
*
I took "x divides y" to mean x/y is an integer.
>* I don't suppose to understand all the math on this page, but I think
*>* it uses the same definition that dvh is using.
*>*
*>* http://mathworld.wolfram.com/GreatestCommonDivisor.html
*
Yes, that's where I got the definition I suggested.
As a concrete example of why I wanted gcd extended to rationals: I wrote
a big-bang program that runs a set of big-bang programs, so it needs a
tick-rate that is the gcd of all the tick-rates of the programs it runs,
which may be rational.
David