[R] understanding all.equal() output: "Mean relative difference"

[Liviu Andronic]

Dear all
How should one parse all.equal() output? I'm specifically referring to
the 'mean relative difference' messages. For example,
> all.equal(pi, 355/113)
[1] "Mean relative difference: 8.491368e-08"

But I'm not sure how to understand these messages. When they're close
to 0 (or 1xe-16), then it's intuitive. But when they're big,
> all.equal(1, 4)
[1] "Mean relative difference: 3"
> all.equal(2, 4)
[1] "Mean relative difference: 1"
> all.equal(3, 4)
[1] "Mean relative difference: 0.3333333"

the messages start making much less sense. I tried Wikipedia [1], but
the description is cryptic, as is the help page. Also, Fox and
Weisberg (2011) don't explain this particular message.

Regards
Liviu

[1] http://en.wikipedia.org/wiki/Mean_difference#Relative_mean_difference


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