Rounding problem R vs Excel

I don't have the reference, but a biologist friend of mine
once showed me a refereed journal article that purported
to demonstrate numerical errors made by MSExcel.  This 
would have been Excel97 or Excel2000... In any case, the
journal's scope was biological in nature and the article 
was of interest since Excel is heavily used in that community.

-david paul

-----Original Message-----
From: Duncan Murdoch [mailto:dmurdoch at pair.com] 
Sent: Wednesday, June 04, 2003 8:34 AM
To: MSchwartz at medanalytics.com
Cc: R-help at stat.math.ethz.ch
Subject: Re: [R] Rounding problem R vs Excel

Excel 2002 (XP):

Cell Formula          Value
= 0.5 - 0.4 - 0.1     0.00000000000000000000E+00
=(0.5 - 0.4 - 0.1)    -2.77555756156289000000E-17

...

What is interesting is the change in the displayed value in Excel when 
the second formula is surrounded by parens (which I found purely by 
accident). This would suggest that there may be something going on in 
the parsing of the cell formula that affects the calculation and 
displayed value.

"Interesting"?  I'd say "horrifying".  When (expr) does not evaluate the
same as expr, what can you trust?

Duncan Murdoch

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