|Bill Allombert on Sat, 20 Oct 2012 17:24:51 +0200|
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On Sat, Oct 20, 2012 at 05:12:22PM +0200, Joerg Arndt wrote: > * Bill Allombert <Bill.Allombert@math.u-bordeaux1.fr> [Oct 19. 2012 20:02]: > > On Fri, Oct 19, 2012 at 05:36:04PM +0200, Karim Belabas wrote: > > > > > > In our normalization, the "0" numeral has no digit. We already have > > > similar behaviour for polynomials : the 0 polynomial has no > > > coefficients. > > > > > > (17:25) gp > Vec(x + 2) \\ Vec(t_POL) returns the polynomial's coeffs > > > %1 = [1, 2] > > > (17:25) gp > Vec(Pol(1,'x)) > > > %2 =  > > > (17:26) gp > Vec(Pol(0,'x)) > > > %3 =  > > > > > > So the current definition of digits() is consistent with what we already do. > > > On the other hand, it is sometimes convenient to consider polynomials > > > with respect to a fixed basis, and "degree drops" are inconvenient. > > > So Vec() has an optional argument to fix the vector length: > > > (17:25) gp > Vec(Pol(1,'x), 5) > > > %4 = [1, 0, 0, 0, 0] \\ 0*x^4 + 0*x^3 + 0*x^2 + 0*x + 1 > > > > Maybe we should return the digits in the other order, so that the relation > > between the indices in the vector and the weight in the number is more > > straightforward. > > Make that an *option*. Well, one can always use Vecrev(digits(n)). Really the question is the standard order. > Similarly with Vec(poly), one should have the choice to get > falling or rising powers (and another option to set the > range of powers would be useful). All of that is implemented, see the function Vec(x,n) and Vecrev(x,n). > While we are at it, the omission of leading zero > coefficients with Vec(powseries) should also be avoidable IMHO > (this ugly-fies much of my code for OEIS sequences). Maybe you can use truncate. Cheers, Bill.