What is 0.14*300?

General Usage
1 
julia> 0.14*300
42.00000000000001

julia> Int32(0.14*300)
ERROR: InexactError: Int32(42.00000000000001)
Stacktrace:
 [1] Int32(x::Float64)
   @ Base .\float.jl:791
 [2] top-level scope
   @ REPL[12]:1

Or for that matter, it seems like 0.14 has a bug with floating point math …

julia> 0.14*50
7.000000000000001

julia> 0.14*100
14.000000000000002

julia> 0.14*40
5.6000000000000005

julia> 0.13*40
5.2

julia> 0.14*2203
308.42

julia> 0.14*10040
1405.6000000000001

julia> 0.14*200
28.000000000000004
2

This is a known limitation with float point operations. There might be some degree of imprecision because the computer does not represent numbers exactly. You will find similar results in Python for example.

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3

So is it safest to always use Int32(round( math )) if an integer is expected?

4

I suspect it depends on the amount of precision you need. You could use Int64 or BigInt if you need more precision. But I am not really an expert at mitigating float point rounding errors. I think if you describe your needs, someone with more expertise might be able to provide sound guidance.

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5

It seems like rational numbers might help with division, but that exhausts my knowledge.

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6

round(Int32, math) is better.

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7

For my error, it was just to go into an argument for an array initialization within a loop, e.g. zeros(Int32( x[i] * 300 )) and when x[i] was 0.14, it was not happy.

8

Gotcha. That might be OK if you are not testing exact equalities in your code. Perhaps you could isapprox, but there might be other or better options for such cases.

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