Re:Julia 1.0
by simonbyrne on Thursday August 09, 2018 @08:05PM
(#17729634)
Well, I have indeed spent more time thinking about this than is probably healthy, but here are some nice edge cases to think about:
- https://github.com/JuliaLang/julia/issues/14826
mod(-eps(), 4.0)
fld(1.0,0.2)
mod(1.0,0.1)
mod(0.95,0.01)
re: mod 2pi, typically it is most accurate to reduce to (-pi,pi) (i.e. division rounding to nearest). Also to get it accurate you need fancy range reduction algorithms, hence julia has rem2pi https://docs.julialang.org/en/stable/base/math/#Base.Math.re...
Without knowing the intended use case of the code, the edge case behavior in some of these cases is pretty meaningless. Different behavior might make sense in different applications, and in many applications the choice is largely irrelevant. Whichever one you choose someone who wants the other version will have to work around it.
These examples don’t really have much bearing on the general usefulness of “remainder” vs. “modulo” though.
As one simple example, it is frequently useful to map floats into the range [0, 2π), but I have never once wanted to map positive floats into the range [0, 2π) while negative floats get mapped into (–2π, 0] by the same code.