JuliaLang/julia

Unconsistent result when using sum or mean function on Complex{Int8} array

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#15,523 opened on Mar 15, 2016

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complexfoldgood first issuemaths

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Description

When using Complex{Int8} arrays, the functions sum and mean do not make proper type conversion to avoid nasty things :

julia> b = ones(Complex{Int8}, 100000) ;

julia> sum(b)
-96 + 0im

julia> mean(b)
-0.00096 + 0.0im

That seems unconsistent with the behaviour of the same functions on Int8 arrays :

julia> a = ones(Int8, 100000) ;

julia> sum(a)
100000

julia> mean(a)
1.0

Contributor guide

Research direction
Look at the implementation of sum and mean in base/sum.jl. Trace the type promotion for Complex{Int8} and identify where overflow occurs. Consider promoting to a wider type before accumulation.
Tech stack
julia
Domain
backend
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Half day
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Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
JuliaGit
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60