Re: poldisc

[Ilya Zakharevich <ilya@math.ohio-state.edu>]

On Thu, Jan 21, 1999 at 03:36:41PM +0100, Karim BELABAS wrote:
> > p=a*x^3+b*x^2*y+c*x*y^2+d*y^3 + e*x^2+f*x*y+g*y^2 + h*x+i*y + h
> > di=poldisc(p)

> PARI's internal representation for polynomials... (highly non-symetrical,
> optimized for 1 or 2 variables).
> 
> It is instantaneous with default stack, *IF* you make sure the
> important variables have high priority:
> gp> y; p=a*x^3+b*x^2*y+c*x*y^2+d*y^3 + e*x^2+f*x*y+g*y^2 + h*x+i*y + h
>    ^^^ (now x and y are priviledged)

What makes y important?  That p has slightly higher degree in y?

Even if I assume that the polynomials are stored as sequences of
coefficients wrt variables, and variables are (by default) ordered by
the order PARI have seen them, the difference between two orderings
still seems to be a transposition of a matrix/tensor.  How may this
affect speed?

Ilya