R devel - Sep 2008 - (PR#12742) Different result with different order of

FAQ 7.31 strikes again.

This is expected: you cannot do exact arithmetic on a binary computer if 
some of the quantities involved are not binary fractions (e.g. 1.3)

See also the warning in ?`==`: identical() is equally inappropiate for 
computed numerical quantities.

On Mon, 8 Sep 2008, kyunseop.bae at gmail.com wrote:
> Full_Name: Kyun-Seop Bae
> Version: 2.7.2
> OS: MS-Windows XP SP2
> Submission from: (NULL) (148.168.40.4)
>
>
> # Script that I used
>
> rm(list=objects())
> objects()
>
> WT <- 91
> AGE <- 41
> SCR <- 1.3
>
> CCL1 <- (140-AGE) * WT / (72 * SCR)
> CCL2 <- (140-AGE) * WT / 72 / SCR
>
> CCL1
> CCL2
>
> identical(CCL1, CCL2)
> identical(CCL1, 96.25)
> identical(CCL2, 96.25)
>
> CCL1*10 + 0.5
> CCL2*10 + 0.5
>
> floor(CCL1*10 + 0.5)
> floor(CCL2*10 + 0.5)
>
> as.integer(CCL1*10 + 0.5)
> as.integer(CCL2*10 + 0.5)
>
>
> # Same with multiplied WT
> # Same in S-Plus Enterprise Developer Version 7.0.6 for Microsoft Windows :
> 2005
> # But these are accurate in MS-Excel.
Unlikely, more likely you don't have identical() to test bit-level 
equality.

-- 
Brian D. Ripley,                  ripley at 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

On Mon, 8 Sep 2008, ksbae wrote:
> Thank you for the prompt reply.
>
> Do you know why does MS-Excel give result that I expected?
Know, but I did comment on that.
>
> Thanks,
>
> Kyun-Seop BAE
> Email: kyunseop.bae at gmail.com
>
>
> -----Original Message-----
> From: Prof Brian Ripley [mailto:ripley at stats.ox.ac.uk]
> Sent: Monday, September 08, 2008 1:53 AM
> To: kyunseop.bae at gmail.com
> Cc: R-bugs at r-project.org
> Subject: Re: [Rd] (PR#12742) Different result with different order of
> binding
>
> FAQ 7.31 strikes again.
>
> This is expected: you cannot do exact arithmetic on a binary computer if
> some of the quantities involved are not binary fractions (e.g. 1.3)
>
> See also the warning in ?`==`: identical() is equally inappropiate for
> computed numerical quantities.
>
> On Mon, 8 Sep 2008, kyunseop.bae at gmail.com wrote:
>
>> Full_Name: Kyun-Seop Bae
>> Version: 2.7.2
>> OS: MS-Windows XP SP2
>> Submission from: (NULL) (148.168.40.4)
>>
>>
>> # Script that I used
>>
>> rm(list=objects())
>> objects()
>>
>> WT <- 91
>> AGE <- 41
>> SCR <- 1.3
>>
>> CCL1 <- (140-AGE) * WT / (72 * SCR)
>> CCL2 <- (140-AGE) * WT / 72 / SCR
>>
>> CCL1
>> CCL2
>>
>> identical(CCL1, CCL2)
>> identical(CCL1, 96.25)
>> identical(CCL2, 96.25)
>>
>> CCL1*10 + 0.5
>> CCL2*10 + 0.5
>>
>> floor(CCL1*10 + 0.5)
>> floor(CCL2*10 + 0.5)
>>
>> as.integer(CCL1*10 + 0.5)
>> as.integer(CCL2*10 + 0.5)
>>
>>
>> # Same with multiplied WT
>> # Same in S-Plus Enterprise Developer Version 7.0.6 for Microsoft
Windows
> :
>> 2005
>> # But these are accurate in MS-Excel.
>
> Unlikely, more likely you don't have identical() to test bit-level
> equality.
>
> -- 
> Brian D. Ripley,                  ripley at 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
>
-- 
Brian D. Ripley,                  ripley at 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