Karim Belabas on Mon, 21 Mar 2005 14:46:33 +0100

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Re: ispower error?

* cino hilliard [2005-03-21 05:30]:
> (14:42) gp > ispower(1)
> *** ispower: isanypower: argument must be > 1.

ispower(x) does not return a boolean value, but the largest exponent k > 1
such that x is a k-th power. This is not defined for x = 1, so the above is

On the other hand ispower(x, 2), with explicit second argument, returns a

Perhaps this is confusing; I hesitated a lot before settling for the
current interface. The other possibility was to split ispower in two

  ispower(x, k, {&n})         \\ k is now mandatory
  issomepower(x, {&n})        \\ for the current ispower(x, /*omitted*/, &n)

I eventually overloaded ispower because I couldn't come up with a
satisfactory name for the is_some_unspecified_power functionnality.

Suggestions/Opinions are welcome.


Karim Belabas                     Tel: (+33) (0)1 69 15 57 48
Dep. de Mathematiques, Bat. 425   Fax: (+33) (0)1 69 15 60 19
Universite Paris-Sud              http://www.math.u-psud.fr/~belabas/
F-91405 Orsay (France)            http://pari.math.u-bordeaux.fr/  [PARI/GP]