Karim BELABAS on Mon, 18 Oct 1999 14:59:08 +0200 (MET DST)

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Re: Lack of error message in Mod

[Jack Fearnley:]
> The Pari manual states that the the first argument of Mod must be an
> integer, scalar or polynomial.
> The following illegal usage 
> Mod(1+O(7^15),7)

It's actually not illegal; the manual was at fault here. I just corrected the
manual; it now reads:

Mod(x,y,{flag = 0}):

     creates the PARI object (x mod y), i.e. an integermod or a polmod.  y
must be an integer or a polynomial.   If y is an integer,  x must be an
integer, a rational number, or a p-adic number compatible with the modulus y.
If y is a polynomial, x must be a scalar, a polynomial, a rational function,
or a power series. [...]

I had to modify slightly the function so that it is consistent with the new
description (power series were not allowed for polynomial modulus, whereas
p-adics were for integral y. It's symmetric now). I also changed the error
message "forbidden type mod I in gmod" which was a bit cryptic.

[all these changes have been committed to the CVS repository]

> Gives an error message in version 2.0.5 but silently returns zero in
> 2.0.16.  It also returns zero for
> Mod(1+)(7^15),3) and Mod(1.0,7)

All of these had been corrected in the last release (2.0.17).


Karim Belabas                    email: Karim.Belabas@math.u-psud.fr
Dep. de Mathematiques, Bat. 425
Universite Paris-Sud             Tel: (00 33) 1 69 15 57 48
F-91405 Orsay (France)           Fax: (00 33) 1 69 15 60 19
PARI/GP Home Page: http://hasse.mathematik.tu-muenchen.de/ntsw/pari/