I have been told by the CRAN administrators that the following code generated
an error on 64-bit Fedora Linux (gcc, clang) and on Solaris machines (sparc,
x86), but runs well on all other systems):
> fn <- function(x, y) ifelse(x^2 + y^2 <= 1, 1 - x^2 - y^2, 0)
> tol <- 1.5e-8
> fy <- function(x) integrate(function(y) fn(x, y), 0, 1,
subdivisions = 300, rel.tol = tol)$value
> Fy <- Vectorize(fy)
> xa <- -1; xb <- 1
> Q <- integrate(Fy, xa, xb,
subdivisions = 300, rel.tol = tol)$value
Error in integrate(Fy, xa, xb, subdivisions = 300, rel.tol = tol) :
roundoff error was detected
Obviously, this realizes a double integration, split up into two 1-dimensional
integrations, and the result shall be pi/4. I wonder what a 'roundoff error'
means in this situation.
In my package, this test worked well, w/o error or warnings, since July 2011,
on Windows, Max OS X, and Ubuntu Linux. I have no chance to test it on one of
the above mentioned systems. Of course, I can simply disable these tests, but
I would not like to do so w/o good reason.
If there is a connection to a bug fix to integrate(), with NEWS item
"integrate() reverts to the pre-2.12.0 behaviour. (PR#15219)",
then I do not understand what this pre-2.12.0 behavior really means.
Thanks for any help or a hint to what shall be changed.
Hans W Borchers
PS:
This kind of tricky definition in function 'fn' has caused some discussion on
this list in July 2009. I still think it should be allowed to proceed in this
way.
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