Re: Constructing polynomials

[Karim Belabas <Karim.Belabas@math.u-psud.fr>]

* Justin Walker [2004-07-22 18:39]:
> I guess I have to plead guilty to aggravated density...

you're welcome.

> On Jul 22, 2004, at 1:18, Karim Belabas wrote:
>>* Justin Walker [2004-07-22 04:53]:
> [snip]
>>>In psuedo-code terms, I'd like to do something like
>>>
>>>MyProc(a,b)=
>>>{
>>>    f(x)=(x+a)^b;
>>>    for (i=1,limit, print(f(i)));
>>>}
>>
>>Why not:
>>
>>  MyProc(a,b)=
>>  {
>>    f=(x+a)^b;
>>    for (i=1,limit, print(subst(f, x, i)));
>>  }
>
> I did try this, but I was working with 't_SER', and subst groused at
> me: "non polynomial or series type substituted in a series".  I could
> make
>    subst(f,x,0*x)
> work, but that's somewhat limited :-}.  Is it possible to 'evaluate' a
> series at a constant in pari/gp?

  subst(truncate(f), x, C)

>>? If you insist on defining a user function, then you can use
>>
>>  MyProc(a,b)=
>>  {
>>    ( f(x) = (x+a)^b );
>>    for (i=1,limit, print(f(i)));
>>  }
>
> This, I'd never have figured out.  For my purposes, it is the better
> alternative.
>
> Why do the "()"s make it acceptable?

I've made a new FAQ entry :-).

  http://www.math.u-psud.fr/~belabas/pari/doc/faq.html#funinfun

In short: the code within parentheses is evaluated first.

Cheers,

    Karim.
--
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]