For example in the code below, x is defining the domain, but why is there the double dot between 0 and 4pi?
using ApproxFun
x=Fun(identity,0..4π)
..
is not part of Julia, rather part of the packages used by ApproxFun
.
It is used to represent intervals, see the code below
julia> u = 1..3
1..3
julia> dump(u)
Interval{:closed,:closed,Int64}
left: Int64 1
right: Int64 3
So this is just a convenience constructor for the Interval
object, see:
julia> 1..3 === Interval{:closed,:closed,Int64}(1,3)
true