R devel - Mar 2005 - zapsmall (PR#7755)

Full_Name: Paul Vos
Version: 2.0.1
OS: windows XP
Submission from: (NULL) (150.216.148.20)

> zapsmall(.3-.2-.1,digits=7)
[1] -2.775558e-17

This should be zero.  By changing the condition
if (mx > 0)
in zapsmall to 
if (mx > 1)
we get
> zapsmall(.3-.2-.1,digits=7)
[1] 0

On Tue, 29 Mar 2005 vosp@mail.ecu.edu wrote:
> Full_Name: Paul Vos
> Version: 2.0.1
> OS: windows XP
> Submission from: (NULL) (150.216.148.20)
>
>
>> zapsmall(.3-.2-.1,digits=7)
> [1] -2.775558e-17
>
> This should be zero.
Why `should' it?  The documentation says:

      'zapsmall' determines a 'digits' argument 'dr' for
calling
      'round(x, digits = dr)' such that values "close to zero"
(compared
      with the maximal absolute one) are "zapped", i.e., treated as
'0'.

That value is not small compared with the maximal absolute one: it is 
equal to it.

-- 
Brian D. Ripley,                  ripley@stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595