RE: apply(sign,x) == x

[Jacques Gélinas <jacquesg00@hotmail.com>]

> returns the polynomial \sum f(a_i) x^i

Thanks for the explanation. This example could be added to ??apply

   ? apply(x->x^2, 4*x^2 + 3*x + 2)

   %3 = 16*x^2 + 9*x + 4

   ? apply(sign, 4*x^2 - 3*x + 2)

   %4 = x^2 - x +1

Jacques Gélinas

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De : Karim Belabas <Karim.Belabas@math.u-bordeaux.fr>
Envoyé : 19 novembre 2018 13:55
À : Jacques Gélinas
Cc : pari-users@pari.math.u-bordeaux.fr
Objet : Re: apply(sign,x) == x

 

* Jacques Gélinas [2018-11-19 19:38]:
> apply(f, A): If A  is  a  polynomial or power series,  apply f on all coefficients.
>
>
> Of course, I would expect sign not to return a polynomial, but -1, 0, or 1 as in
>
>
> apply(sign,Vec(x)) == [1,0]

apply(f, a t_POL \sum a_i x^i) applies f to each coefficient,
i.e. it returns the polynomial \sum f(a_i) x^i

? apply(n->n+1,'x)
%1 = 2*x + 1

Cheers,

    K.B.
--
Karim Belabas, IMB (UMR 5251)  Tel: (+33) (0)5 40 00 26 17
Universite de Bordeaux         Fax: (+33) (0)5 40 00 21 23
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