Karim Belabas on Mon, 08 Feb 2010 13:52:05 +0100 |
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Re: thue() wants more than 4GB stack |
* Max Alekseyev [2010-02-05 19:27]: > I wonder whether this behavior is intended? > > ? thue(thueinit(-3711916*x^4 - 161330*x^3 + 178491*x^2 - 365*x - 19),344622096) > *** thue: Warning: Non trivial conditional class group. > *** The result returned by 'thue' is conditional on the GRH. > *** at top-level: thue(thueinit(-37119 > *** ^-------------------- > *** thue: the PARI stack overflows ! > current stack size: 4294967296 (4096.000 Mbytes) > [hint] you can increase GP stack with allocatemem() Intended, no. Expected, yes :-) > This is rather unusual example since many other thue() computations I > performed were not so eager for memory. After a simple change of variable, the algorithm needs to solve K = bnfinit(x^4+365*x^3-3391329*x^2+58240130*x+25460031844); a = -461794186226632896; bnfisintnorm(K, a) Unfortunately, 'a' has many prime divisors (with moderately large valuations), in fact 18 prime ideal divisors, producing a huge number of potential solutions, about half of which should yield actual solutions since the class number of K is 2. It is not clean whether these solutions can actually fit in physical memory (I'll double check this, maybe there is some simple obstruction and no solution after all...). Cheers, K.B. -- Karim Belabas, IMB (UMR 5251) Tel: (+33) (0)5 40 00 26 17 Universite Bordeaux 1 Fax: (+33) (0)5 40 00 69 50 351, cours de la Liberation http://www.math.u-bordeaux.fr/~belabas/ F-33405 Talence (France) http://pari.math.u-bordeaux.fr/ [PARI/GP] `