Bill Allombert on Mon, 17 Mar 2003 23:47:14 +0100 |
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Re: QX_caract |
On Sat, Mar 15, 2003 at 03:29:46PM +0100, Karim BELABAS wrote: > On Wed, 5 Mar 2003, Bill Allombert wrote: > > Why not use the modular algorithm of ZX_caract directly in QX_caract > > instead of removing the content and calling ZX_caract ? > [...] > > Of course I have not addressed how to implement this, in particular > > how to know we have a sufficiently large modulus. > > For this to work, the result needs to be in Z[X], wich is not the current > specification of QX_caract. ... or we know a multiple of the denominator, or we can use ratlift. Furthermore I am specially interested by polred() in which this assumption is correct. > OK, this is implemented in CVS. The modulus bound is rigorous (~ Hadamard > bound + floating point computation if bound is huge). Thanks ! I have tried it and polred seems to be much faster on my degree 72 polynomials. At least it use a bound of 2^16000 instead of 2^3000000 (72 times...). Of course this is still much too large or else polred is a complete failure (we expect polred to give small polynomial after all), but at least this is bearable. (it take 9 minutes instead of 7 hours.) Cheers, Bill