The issue is that float(pi) < 100*(pi/100). The fact that pi is not rational – or rather, that float64(pi) cannot be expressed as the division of two 24-bit integers as a 64-bit float – prevents rational lifting of the range from kicking in. I worried about this kind of issue when I was working on FloatRanges, but I'm not sure what you can really do, aside from hacks where you just decide that things are "close enough" based on some ad hoc notion of close enough (Matlab uses 3 ulps). For example, you can't notice that pi/(pi/100) is an integer – because it isn't:
julia> pi/(pi/100) 99.99999999999999 One approach is to try to find a real value x such that float64(x/100) == float64(pi)/100 and float64(x) == float64(pi). If any such value exists, it makes sense to do a lifted FloatRange instead of the default naive stepping seen here. In this case there obviously exists such a real number – π itself is one such value. However, that doesn't quite solve the problem since many such values exist and they don't necessarily all produce the same range values – which one should be used? In this case, π is a good guess, but only because we know that's a special and important number. Adding in ad hoc special values isn't really satisfying or acceptable. It would be nice to give the right behavior in cases where there is only one possible range that could have been intended (despite there being many values of x), but I haven't figured out how determine if that is the case or not. The current code handles the relatively straightforward case where the start, step and stop values are all rational. On Wed, Apr 23, 2014 at 5:59 PM, Peter Simon <psimon0...@gmail.com> wrote: > The first three results below are what I expected. The fourth result > surprised me: > > julia> (0:pi:pi)[end] > 3.141592653589793 > > julia> (0:pi/2:pi)[end] > 3.141592653589793 > > julia> (0:pi/3:pi)[end] > 3.141592653589793 > > julia> (0:pi/100:pi)[end] > 3.1101767270538954 > > Is this behavior correct? > > Version info: > julia> versioninfo() > Julia Version 0.3.0-prerelease+2703 > Commit 942ae42* (2014-04-22 18:57 UTC) > Platform Info: > System: Windows (x86_64-w64-mingw32) > CPU: Intel(R) Core(TM) i7 CPU 860 @ 2.80GHz > WORD_SIZE: 64 > BLAS: libopenblas (USE64BITINT DYNAMIC_ARCH NO_AFFINITY) > LAPACK: libopenblas > LIBM: libopenlibm > > > --Peter > >
