[R] question about precision, floor, and powers of two.

[Uwe Ligges]

Dr Carbon wrote:

> At the risk of being beaten about the face and body, can somebody explain
> why the middle example: log2(2^3); floor(log2(2^3)) is different than
> examples 1 and 3?


Because

 > log2(2^3) - 3
[1] -4.440892e-16

see the R FAQ "Why doesn't R think these numbers are equal?".

Uwe Ligges

> 
>>log2(2^2); floor(log2(2^2))
> 
> [1] 2
> [1] 2
> 
>>log2(2^3); floor(log2(2^3))
> 
> [1] 3
> [1] 2
> 
>>log2(2^4); floor(log2(2^4))
> 
> [1] 4
> [1] 4
> 
> 
> DrC
> 
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