Hi! On Mon, Nov 08, 2004 at 12:45:41PM +0100, Ralf Stephan wrote:
To declare something as cofactor does not mean it is. What the function returns does NOT satisfy the usual cofactor equation
gcd(a,b) = ca*a + cb*b.
These are not the cofactors (at least, I've never seen the quantities from this equation referred to as "cofactors"). The cofactors in GiNaC's gcd() are defined by a = ca*gcd(a,b) -> ca = a/gcd(a,b) b = cb*gcd(a,b) -> cb = b/gcd(a,b) Like many other things in GiNaC, this follows the behavior of Maple. What you want (the solutions to s,t in gcd(a,b)=s*a+t*b) is indeed something entirely different, and computed by a different algorithm (gcdex() in Maple).
Vide my earlier example, or a = (x-1)(x+1), b = (x-1)^3 which should give ca = (3-x)/4 and cb = 1/4. But it gives ca = (1-x)^2, cb = 1+x.
(It actually gives ca=1+x, cb=(1-x)^2.) Bye, Christian -- / Physics is an algorithm \/ http://www.uni-mainz.de/~bauec002/