Karim Belabas on Mon, 28 Jun 2010 12:14:52 +0200


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Re: Precision of power series 

* Xavier Roblot [2010-06-28 09:53]:
> Dear PARI users,
> 
> Does anybody know how to get in GP the precision of a power series?
> That is, if the power series is X+O(X^20) say, I am looking for a
> function that would return 20.

Actually, I'd rather return 19 since your series has valuation 1 and only
19 significant terms are known. That you can get with 

  s = X + O(X^20);
  length(s)

or simply

  #s

If you really want the 20 above, then use (#s + valuation(s, 'X)). Both
also work for trivial power series O(X^n), with 0 sigificant terms.

Cheers,

    K.B.
--
Karim Belabas, IMB (UMR 5251)  Tel: (+33) (0)5 40 00 26 17
Universite Bordeaux 1          Fax: (+33) (0)5 40 00 69 50
351, cours de la Liberation    http://www.math.u-bordeaux1.fr/~belabas/
F-33405 Talence (France)       http://pari.math.u-bordeaux1.fr/  [PARI/GP]
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