Re: Bug in default

[Gerhard Niklasch <nikl@mathematik.tu-muenchen.de>]

In response to:
> Message-ID: <20000509025722.A17225@monk.mps.ohio-state.edu>
> Date: Tue, 9 May 2000 02:57:22 -0400
> From: Ilya Zakharevich <ilya@math.ohio-state.edu>
> To: Jack Fearnley <jack@alcor.concordia.ca>
> Cc: pari-dev@list.cr.yp.to
> References: <3.0.1.32.20000508222452.00688eac@alcor.concordia.ca>
> 
> On Mon, May 08, 2000 at 10:24:52PM -0400, Jack Fearnley wrote:
> > ? default(format,"g0.7")
> >    format = g0.7
> > ? default(realprecision)
> >    realprecision = 28 significant digits (7 digits displayed)
> > ? default(realprecision,,1)
> > %2 = 7
> > ?
> > *********************************************************************
> > While computation is proceeding with the correct realprecision (28 in this
> > case) the function call
> > default(realprecision,,1) is returning 7 which is the displayed number of
> > digits.

This is a feature.  In fact, the opposite question was asked recently.
Cf. postings D-000900, D-000901 from the turn March/April.

precision(x) is what you're looking for.

Note that in certain circumstances, the precision of a result may
be larger or smaller than the default realprecision's underlying
number of digits -- compare precision(1.) to precision (1+0.) .
Use the former to recover the default value.  Use precision(x) to
find out to what precision x has in fact been computed.

> This is related to another problem: when you request calculations with
> 7 digits, they are done with 9 (as they should), but the info that you
> in fact requested 7 is not stored anywhere.

Of course it is stored somewhere -- this is just what Jack has been
pointing out! :)

Enjoy, Gerhard