Michael Somos on Fri, 3 Dec 1999 12:33:50 -0500 (EST)

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Re: power series bug?

Karim wrote :

> Strictly speaking it's not a bug since the result is correct (0 is indeed
> O(t)). On the other hand, given the input, it could have been more precise.
> It comes from Karatsuba multiplication and the annoying fact that
> when the entries are approximate. I don't see any way of correcting this
> besides disabling fast multiplication when the entries are not exact, and we
> don't want that. I can fix this particular case though: factor out x first,
> multiply what's left, then multiply back by x^n.

Given the highly unexpected behavior of PARI/GP with a simple
multiplication, I have a suggestion and a proposal.

1. I suggest creating and maintaining a list of unexpected behavior
   so that the user could be forewarned about this. This would help
   to prevent bug reports about features which are unexpected. As of
   now, I don't know what is or is not expected behavior.

2. I would like to propose an option to turn off Karatsuba multiplication
   if the user requests it. This would help a user to avoid undesired
   behavior of multiplication. It would not prevent users from gaining
   the benefits of Karatsuba by default.

Shalom, Michael

Michael Somos <somos@grail.cba.csuohio.edu>     Cleveland State University
http://grail.cba.csuohio.edu/~somos/            Cleveland, Ohio, USA 44115