Karim Belabas on Wed, 26 Nov 2014 23:50:14 +0100

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Re: new GP functions varhigher / varlower

* Karim Belabas [2014-11-26 19:11]:
> I spent some time with Bill to allow variables of arbitrary priorities
> in libpari, then GP. There were discussions on pari-dev, originating e.g. in
> 6) [TODO] We need a variables(T) function that returns the list of
> variables used in T: with variable(T) we can get the variable of highest
> priority occuring in T, but it's very hard to get the variable of lowest
> priority. It's useful to obtain e.g. a variable of lower priority than
> all variables occuring in T without using up a variable number to create
> a *new* variables with guaranteed lowest priority.

That one is now committed in master:

  ? v=x*y+O(x)+Mod(y*a*z,y^2+1)*t/(y+t);
  ? variables(v)
  %2 = [x, y, z, t, a]
  ? tt=varlower("y",x);
  ? zz=varhigher("y",x);
  ? variables([v,tt,zz])
  %5 = [y, x, y, z, t, a]

It's unfortunate to have two functions named variable() [ the historical one ]
and variables() [ the new one ], but I couldn't come up with a better name
in the PARI style, i.e. VariablesInObject is not an option :-).

Suggestions ?


Karim Belabas, IMB (UMR 5251)  Tel: (+33) (0)5 40 00 26 17
Universite de Bordeaux         Fax: (+33) (0)5 40 00 69 50
351, cours de la Liberation    http://www.math.u-bordeaux1.fr/~kbelabas/
F-33405 Talence (France)       http://pari.math.u-bordeaux1.fr/  [PARI/GP]