[R] Numbers that look equal, should be equal, but if() doesn't see as equal (repost with code included)

Paul Lemmens P.Lemmens at nici.kun.nl
Wed May 28 16:35:59 CEST 2003

Hoi Thomas,

--On woensdag 28 mei 2003 7:16 -0700 Thomas Lumley 
<tlumley at u.washington.edu> wrote:

> On Wed, 28 May 2003, Paul Lemmens wrote:
>> Hi!
>> Apologies for sending the mail without any code. Apparently somewhere
>> along the way the .R attachments got filtered out. I have included the
>> code below as clean as possible. My original mail is below the code.
> I still think you need not to be using ==.  You want something like
> if ( abs(mean.b-mean.orig)/(epsilon+abs(mean.orig) < epsilon){
> You are effectively using epsilon=0, but epsilon=10e-10 should be
> adequate.
Based on all the hints and explanations I've changed the test to 
'identical(all.equal(mean.b, mean.orig, tolerance=.Machine$double.eps), 

I still need to look into the concept of finite precision, because I still 
don't grasp how sometimes (as an extreme example, probably) 0.25 != 1/4. 
That this will happen for a number with a lot of different decimals I can 
understand (by an accumulation of rounding errors).

thnx all 4 your help!

Paul Lemmens
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