Bill Allombert on Mon, 14 Oct 2002 23:17:12 +0200 |
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Re: bug in polredabs? |
On Mon, Oct 14, 2002 at 10:32:25AM -0700, Carl R. Witty wrote: > Version: Debian packages version 2.1.4-1 (x86 linux). > > I'm trying to do exactly the same thing, except with different > polynomials. Here's my example: > > I was hoping, based on the polcompositum example, that the last line > would return 0; this would have worked if the second element returned > by polredabs were 7/6*x instead of 7*x. You are right this is a bug, and it is fixed in the development release. This come from the fact that your polynomial is not monic and so polredabs need to convert it to a monic one (definining the same field) internaly but forget to fix the output. > Should this work? And if not, is there a way to do what I want? > ? z = polcompositum(x^2-3, 12*x^2-1, 1)[1]; What is it meant for ? x^2-3 and 12*x^2-1 define the same field (Q(sqrt(3))) > ? pol = z[1] > %2 = 12*x^2 - 49 You get a third definition of the same field... > ? a = z[2]; a^2-3 > %3 = 0 > ? z = polredabs(pol, 1); > ? pol = z[1] > %5 = x^2 - 3 You get the definition you had at the start! > ? a = subst(a.pol, x, z[2]) OK polredabs(,1) is buggy so a is wrong here. Maybe what you want to do is ? z = factornf(12*x^2-1,y^2-3) %1 = [Mod(1, y^2 - 3)*x + Mod(-1/6*y, y^2 - 3) 1] [Mod(1, y^2 - 3)*x + Mod(1/6*y, y^2 - 3) 1] ? a=lift(-subst(z[1,1],x,0)) %2 = 1/6*y Cheers, Bill