From: Duncan Murdoch <murdoch.duncan_at_gmail.com>

Date: Fri, 27 Jan 2012 13:26:17 -0500

> Well, for some definition of 'incorrectly'. It is clearly what the

*> author of that piece of code intended.
*

> It would be helpful if people would cite definitive references. Someone

*> is going to have to report this on the bugtracker, and at present I
*

*> don't have enough evidence to do so: the C99/C11 standards do not seem
*

*> to mandate a particular value (they do say what happens for values less
*

*> than zero, but C compilers are allowed to have or not have signed
*

*> zeroes). (Various Unix-alikes say what they do, usually -0, but that's
*

*> not evidence that other answers are 'incorrect'.)
*

R-devel_at_r-project.org mailing list

https://stat.ethz.ch/mailman/listinfo/r-devel Received on Fri 27 Jan 2012 - 18:30:34 GMT

Date: Fri, 27 Jan 2012 13:26:17 -0500

On 27/01/2012 12:32 PM, Prof Brian Ripley wrote:

> On 27/01/2012 13:26, Duncan Murdoch wrote:

*> > On 12-01-27 7:23 AM, Hans W Borchers wrote:
**> >> I have a question concerning the new Windows toolchain for R>= 2.14.2.
**> >> When trying out my package 'pracma' on the win-builder development
**> >> version
**> >> it will stop with the following error message:
**> >>
**> >> > f3<- function(x, y) sqrt((1 - (x^2 + y^2)) * (x^2 + y^2<= 1))
**> >> > dblquad(f3, -1, 1, -1, 1) # 2.094395124 , i.e. 2/3*pi , err = 2e-8
**> >> Warning in sqrt((1 - (x^2 + y^2)) * (x^2 + y^2<= 1)) : NaNs produced
**> >> Warning in sqrt((1 - (x^2 + y^2)) * (x^2 + y^2<= 1)) : NaNs produced
**> >> Error in integrate(function(y) f(x, y), ya, yb, subdivisions = subdivs, :
**> >> non-finite function value
**> >> Calls: dblquad ...
**> >> <Anonymous> -> f -> do.call -> mapply -> <Anonymous> -> integrate
**> >> Execution halted
**> >> ** running examples for arch 'x64' ... ERROR
**> >> Running examples in 'pracma-Ex.R' failed
**> >>
**> >> This probably means that the following expression got negative for some
**> >> values x, y:
**> >>
**> >> (1 - (x^2 + y^2)) * (x^2 + y^2<= 1)
**> >
**> > I think you're right, it's a bug, hopefully easy to fix. Here's a
**> > simpler version:
**> >
**> > x<- 0*(-1)
**> > sqrt(x)
**> >
**> > x is a "negative zero", and the sqrt() function incorrectly produces a
**> > NaN in the new toolchain.
*

>

> Well, for some definition of 'incorrectly'. It is clearly what the

>

> It would be helpful if people would cite definitive references. Someone

Section 6.3 of IEEE 754-2008 says

Except that squareRoot(−0) shall be −0, every numeric squareRoot result shall have a positive sign.

Duncan Murdoch

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https://stat.ethz.ch/mailman/listinfo/r-devel Received on Fri 27 Jan 2012 - 18:30:34 GMT

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