[R] Precision level

[Rolf Turner]

On 26/03/2010, at 12:38 PM, jim holtman wrote:

> WHen using '==' or '%in%' it is a equality test -- it has to equal zero.  If
> you want a tolerance in the test, use 'all.equal'
> 
> On Thu, Mar 25, 2010 at 5:29 PM, Dimitri Liakhovitski <ld7631 at gmail.com>wrote:
> 
>> Hello!
>> 
>> I am wondering at what point does R consider a numeric value to be
>> equal to zero - for statements of the type x==0 and x %in% 0.
>> 
>> Thank you very much!


There is still perhaps a question to be answered here.  One can key in
a representation of a number, different from ``0'' and yet get a value
deemed to be 0 by the machine.

E.g. on my machine
> 1e-324 == 0
[1] TRUE
> 1e-323 == 0
[1] FALSE

The question of where the line is drawn is probably ill-posed or meaningless
or something like that.  It's not clear to me what the issues are.  Also the
answer, if there is a meaningful one, is likely to be machine dependent rather
than R dependent.

	cheers,

		Rolf Turner

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