[GiNaC-devel] Univarite GCD timing correction

[Alexei Sheplyakov]

Hi,

On Mon, Feb 09, 2009 at 11:08:49AM +0100, Jens Vollinga wrote:
> I did read your remark
>
> > much more severe bug (in multivariate GCD code). I'll fix the test
> > after I find out what is wrong with chinrem_gcd().
>
> and are waiting with the release, of course, until this issue is settled.

On Mon, Feb 09, 2009 at 08:22:47PM +0100, Richard B. Kreckel wrote:
> For the record, here's what I did:
> $ git checkout master~9
> This left me with "HEAD is now at 45b1e47... Implement modular
> multivariate GCD (based on chinese remaindering algorithm)." I applied
> you "patch", made check and it hang at the same point that has been
> reported before by Jens and Vladimir on 32-bit systems.

Now I believe my theory and the fix for poly_cra() are correct. Please find
the patch fixing the univarite GCD timing below.

From: Alexei Sheplyakov <varg at metalica.kh.ua>
Subject: [PATCH] Univariate GCD timing: use sr_gcd when appropriate.

The benchmark consists of two parts:
1) timing of different GCD calculation methods (i.e. subresultant PRS,
   heuristic, chinese remaindering).
2) timing of different implementations of the same method. The purpose
   is to find out how (in)efficient GiNaC::ex is as a representation
   of (univariate) polynomials (as a side note, the result is a bit
   depressing -- using coefficient vector instead of GiNaC:ex makes
   GCD calculation 50x -- 1000x faster).

Now GiNaC uses modular (chinese remaindering) GCD by default, so part 2)
got broken, i.e. instead of (intended) timings

a) (heuristic, GiNaC::ex) versus (heuristic, coefficient vector)
b) (PRS, GiNaC::ex) versus (PRS, coefficient vector)

one gets

a') (heuristic, GiNaC::ex) versus (heuristic, coefficient vector)
b') (chinese remaindering, GiNaC::ex) versus (PRS, coefficient vector)

Set the gcd_options::use_sr_gcd to restore the meaning of the benchmark.

Note: this patch does not affect the library proper.

---
 check/time_uvar_gcd.cpp |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/check/time_uvar_gcd.cpp b/check/time_uvar_gcd.cpp
index c65c515..fe75897 100644
--- a/check/time_uvar_gcd.cpp
+++ b/check/time_uvar_gcd.cpp
@@ -1780,7 +1780,8 @@ struct ex_sr_gcd_test
 	const upoly& g_check;
 	unsigned options;
 	ex_sr_gcd_test(const ex& a_, const ex& b_, const upoly& g_) :
-		a(a_), b(b_), g(0), g_check(g_), options(gcd_options::no_heur_gcd)
+		a(a_), b(b_), g(0), g_check(g_), options(gcd_options::no_heur_gcd |
+				                         gcd_options::use_sr_gcd)
 	{ }
 
 	inline void run()
-- 
1.5.6.5


Best regards,
	Alexei

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