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