Charles Greathouse on Mon, 22 Feb 2010 19:18:22 +0100

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 Re: Getting the variable number of a lexical local variable

```> The prototype code V is for functions that use the code E or I.
> Such local variables are not formal variables and does not have a
> formal variable number (but they have a lexical variable number).

I guess what I was trying to find was the lexical variable number,
then.  I do want to use a V prototype code so that a user (in GP) can
type
sumformal(y=1, n, x*y^3 + y)
and I can pull the relevant variable out of the polynomial.

Charles Greathouse
Analyst/Programmer
Case Western Reserve University

On Mon, Feb 22, 2010 at 11:42 AM, Bill Allombert
<Bill.Allombert@math.u-bordeaux1.fr> wrote:
> On Sun, Feb 21, 2010 at 11:47:14PM -0500, Charles Greathouse wrote:
>> I still can't seem to make it work properly with multiple variables.
>> If I'm in a loop with formal variable y and I check polcoeff0(expr, 3,
>> -1) with expr = 3*y + 5*x, it gives me 5, not 3.  I would like a way
>> to get 3 when the formal variable is y and 5 when the formal variable
>> is x.  Can this be done?
>
> You should not use the prototype code V, but the code n instead.
> This will give you the formal variable number (your function need to
> take an extra argument of type 'long int').
>
> The prototype code V is for functions that use the code E or I.
> Such local variables are not formal variables and does not have a
> formal variable number (but they have a lexical variable number).
>
> There are two very different notions:
> 1) formal variables and polynomials expressions
> 2) GP variable and GP code.
>
> for 1) you use the code n, G and the function subst (or poleval, etc.)
> for 2) you use the code V, E and push_lex/set_lex and closure_evalvoid/closure_evalgen.
>
>> I've attached my source, if this would help anyone understand what I'm
>> doing.  Faulhaber(n, a) returns the n-Faulhaber polynomial (in a).
>>
>> GEN
>> sumformal(GEN start, GEN end, GEN expr)
>
> What is prototype code do you use ?
>
> I would suggest to use  "nGGG" and change the prototype to:
> sumformal(long vy, GEN start, GEN end, GEN expr)
> (vy will be the variable number of y).
>
> Cheers,
> Bill.
>

```