Bill Allombert on Wed, 28 Jun 2006 20:56:07 +0200

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Re: divrem bug?

On Wed, Jun 28, 2006 at 08:30:39PM +0200, Bernard Parisse wrote:
> Bill Allombert wrote:
> >On Wed, Jun 28, 2006 at 02:58:57PM +0200, Bernard Parisse wrote:
> >
> >>Hi!
> >>
> >>under pari 2.3.0, divrem(x+1,x^2,y) returns 
> >>%1 = [1/y^2*x + 1/y^2, 0]
> >>
> >>It should be something corresponding to [(x+1)/x^2, 0], 
> >>y should not occur there. Or is it not handled under pari?
> >
> >
> >Well returning incorrect output is a bug but I would not expect
> >divrem(x+1,x^2,y) to work because this breaks variable priorities.
> >
> Does it mean that divrem only works when the optionnal 3rd arg is the
> main variable? In that case, the default argument should probably be
> omitted.

It works only if the optional 3rd arg has higher priority:

? divrem(y+1,y^2,x)
%1 = [(y + 1)/y^2, 0]~
? divrem(y+1,y^2,y)
%2 = [0, y + 1]~

This still useful.

> Otherwise, I believe that the fix should be in the C divrem function,
> it should reorder variables before doing the division.

Experimentally doing that almost always break something due to 
t_POLMOD objects.

> I have a question about the documentation: currently I'm using
> the short on-line doc available from src/language/init.h, but I would

Please extract it from the pari.desc file instead.
(We provide a perl module PARI::822 for that purpose).

> like to have HTML online doc like for native xcas functions (currently
> only in French), is there a way to convert the PARI tex doc using
> something like latex2html?

Please see
However gphtml only display the long help of functions, not the manual
body text.

PARI doc is in TeX, not in LaTeX so latex2html will not work.