Possible issue with "println" or with control flow

[papamarkou]

I run the following naive "for" loop in order to check that I can iterate with a step size of my own preference (0.1 in this example):

for i = 1:0.1:2
println(i)
end

and I got the following output:

1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.7000000000000002
1.8
1.9
2.0

I suspect it has to do with "println", because the comprehension

[i for i= 1:0.1:2]

prints out 1.7 instead of 1.7000000000000002:

11-element Float64 Array:
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2.0

This is not necessarily a bug, it may be my lack of understanding. I was simply puzzled, since I was expecting 1.7 to be printed via "println" instead of 1.7000000000000002.

[JeffBezanson]

Array elements are printed with less precision:

julia> a=[i for i= 1:0.1:2]
11-element Float64 Array:
 1.0
 1.1
 1.2
 1.3
 1.4
 1.5
 1.6
 1.7
 1.8
 1.9
 2.0

julia> a[8]
1.7000000000000002

We could possibly print vectors with full precision as a special case, since there is room for it.

[StefanKarpinski]

See also #2333. If we integrate some of those fixes to ranges, which I have lying around on a branch somewhere, then this problem actually won't occur since you will get precisely 1.7 to the best possible floating-point representation.

[papamarkou]

Thank you both Stefan and Jeff, #2333 was helpful in understanding the source of the problem.