[Rd] Friday question: negative zero

From: Duncan Murdoch <murdoch_at_stats.uwo.ca>
Date: Fri, 31 Aug 2007 20:39:02 -0400

The IEEE floating point standard allows for negative zero, but it's hard to know that you have one in R. One reliable test is to take the reciprocal. For example,

> y <- 0
> 1/y
[1] Inf
> y <- -y
> 1/y
[1] -Inf

The other day I came across one in complex numbers, and it took me a while to figure out that negative zero was what was happening:

  > x <- complex(real = -1)
  > x
[1] -1+0i
  > 1/x
[1] -1+0i
  > x^(1/3)
[1] 0.5+0.8660254i
  > (1/x)^(1/3)
[1] 0.5-0.8660254i

(The imaginary part of 1/x is negative zero.)

As a Friday question: are there other ways to create and detect negative zero in R?

And another somewhat more serious question: is the behaviour of negative zero consistent across platforms? (The calculations above were done in Windows in R-devel.)

Duncan Murdoch

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