Bill Allombert on Thu, 24 Dec 2009 14:58:57 +0100 |
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Re: How to implement equivalent of magma NullSpace in Pari/GP |
On Thu, Dec 24, 2009 at 11:30:07AM +0000, John Cremona wrote: > 2009/12/24 Bill Allombert <Bill.Allombert@math.u-bordeaux1.fr>: > > Really ? If you want to compute the kernel over Z/2Z then you should do > > matker(M*Mod(1,2)). > > Perhaps not "should": from the documentation of matker, > > Note: The library function FpM_ker(x, p), where x has integer > entries reduced mod p and p is > prime, is equivalent to, but orders of magnitude faster than, > matker(x*Mod(1,p)) and needs much > less stack space. To use it under gp, type install(FpM_ker, GG) first. Your suggestion is good, thought matker in the PARI development branch will automatically call FpM_ker if the matrix is filled with intmod. However the interface of FpM_ker can be more convenient and less wasteful. The development branch also include a function F2m_ker for matrix over GF(2) (which is used internally by FpM_ker) but it use a different input format (one bit per entry). Cheers, Bill.