Re: [sage-devel] Re: gcd vs xgcd

2015-02-16 Thread Bill Hart
On Monday, 16 February 2015 12:01:31 UTC+1, Jeroen Demeyer wrote: > > On 2015-02-14 16:40, Bill Hart wrote: > > Wikipedia claims that it is possible to compute gcd in R[x] for any > > unique factorisation domain R. But in thinking about it last night, I > > couldn't see why the algorithm doesn

Re: [sage-devel] Re: gcd vs xgcd

2015-02-16 Thread Jeroen Demeyer
On 2015-02-14 16:40, Bill Hart wrote: Wikipedia claims that it is possible to compute gcd in R[x] for any unique factorisation domain R. But in thinking about it last night, I couldn't see why the algorithm doesn't work in any GCD domain R. Perhaps it works for GCD domains, but the proofs are ha

Re: [sage-devel] Re: gcd vs xgcd

2015-02-14 Thread Bill Hart
Slightly OT post, more about polynomial GCD than the original question: The flint fmpz_poly_xgcd function is badly named. It should be fmpz_poly_bezout. We might even change it in a later release. The point is, the result of the Euclidean algorithm in the case of Z[x] is not the gcd, but the re

Re: [sage-devel] Re: gcd vs xgcd

2015-02-12 Thread Bruno Grenet
Le 12/02/2015 16:06, kcrisman a écrit : As a late postscript, is #8111 related to any of this discussion? I know this was mostly about Bezout/xgcd stuff, but that ticket looks like it has languished and could be connected. This is clearly the same kind of discussions. The point in #8111 is that

Re: [sage-devel] Re: gcd vs xgcd

2015-02-12 Thread kcrisman
As a late postscript, is #8111 related to any of this discussion? I know this was mostly about Bezout/xgcd stuff, but that ticket looks like it has languished and could be connected. - kcrisman -- You received this message because you are subscribed to the Google Groups "sage-devel" group. T

Re: [sage-devel] Re: gcd vs xgcd

2015-01-26 Thread Bruno Grenet
Le 26/01/2015 18:06, Vincent Delecroix a écrit : 2015-01-26 17:07 UTC+01:00, Jeroen Demeyer : On 2015-01-26 14:22, Bruno Grenet wrote: In the special case of univariate polynomials over ZZ, I think there are two possibilities for xgcd: - either xgcd(p,q) = (g,u,v) where g = gcd(p,q) = up+vq w

Re: [sage-devel] Re: gcd vs xgcd

2015-01-26 Thread Vincent Delecroix
2015-01-26 17:07 UTC+01:00, Jeroen Demeyer : > On 2015-01-26 14:22, Bruno Grenet wrote: >> In the special case of univariate polynomials over ZZ, I think there are >> two possibilities for xgcd: >> >> - either xgcd(p,q) = (g,u,v) where g = gcd(p,q) = up+vq with u,v in >> QQ[x]; >> - or xgcd(p,q) =

Re: [sage-devel] Re: gcd vs xgcd

2015-01-26 Thread Jeroen Demeyer
On 2015-01-26 14:22, Bruno Grenet wrote: In the special case of univariate polynomials over ZZ, I think there are two possibilities for xgcd: - either xgcd(p,q) = (g,u,v) where g = gcd(p,q) = up+vq with u,v in QQ[x]; - or xgcd(p,q) = (g×r, u, v) where g = gcd(p,q), r = res(p,q), g×r = up+vq with

Re: [sage-devel] Re: gcd vs xgcd

2015-01-26 Thread Bruno Grenet
Le 26/01/2015 14:41, Vincent Delecroix a écrit : Hello, 2015-01-26 14:22 UTC+01:00, Bruno Grenet : In the special case of univariate polynomials over ZZ, I think there are two possibilities for xgcd: - either xgcd(p,q) = (g,u,v) where g = gcd(p,q) = up+vq with u,v in QQ[x]; - or xgcd(p,q) = (

Re: [sage-devel] Re: gcd vs xgcd

2015-01-26 Thread Vincent Delecroix
Hello, 2015-01-26 14:22 UTC+01:00, Bruno Grenet : > In the special case of univariate polynomials over ZZ, I think there are > two possibilities for xgcd: > > - either xgcd(p,q) = (g,u,v) where g = gcd(p,q) = up+vq with u,v in QQ[x]; > - or xgcd(p,q) = (g×r, u, v) where g = gcd(p,q), r = res(p,q),

Re: [sage-devel] Re: gcd vs xgcd

2015-01-26 Thread Bruno Grenet
Salut ! I disagree with John and Jeroen that xgcd should not be defined or should return an error for non-PID UFDs. For now, I checked the possibilities for the rings of polynomials over a UFD. In the special case of univariate polynomials over ZZ, I think there are two possibilities for xgc

[sage-devel] Re: gcd vs xgcd

2015-01-26 Thread mmarco
Anyways, we should take into account that, even when both gcd and xgcd are well defined, their definition coincide and everything is happy... there are still defined only up to product of a unit. So there is yet another possible source of inconsistency. El domingo, 25 de enero de 2015, 21:05:00