JuliaPhysics/Unitful.jl

Idea for definition of conversion constants

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#81 opened on May 12, 2017

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enhancementhelp wanted

Description

Currently, the package isn't very arbitrary-precision-friendly, because conversion constants are often of Float64 type. My idea is to define them as Irrational:

julia> using Unitful

julia> Base.@irrational μ 1.256637061435917295385e-06 (4 * big(π) * (1//10) ^ 7)

julia> μ0 = μ * Unitful.H / Unitful.m 
μ = 1.2566370614359... H m^-1

julia> float(μ)
1.2566370614359173e-6

julia> float(Unitful.μ0.val)
1.2566370614359173e-6

julia> big(μ)
1.256637061435917295385057353311801153678867759750042328389977836923126562514468e-06

julia> big(float(μ))
1.256637061435917288506887261323452520400678622536361217498779296875000000000000e-06

julia> big(Unitful.μ0.val)
1.256637061435917288506887261323452520400678622536361217498779296875000000000000e-06

The last three lines show that in this way the conversion factor has full precision as a BigFloat.

Edit: I initially proposed to define a type that was a simplification of Irrational, but in the end there wasn't much difference between my custom type and Irrational.

Contributor guide

Tech stack
None
Domain
performance
Issue type
feature
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.
3-5 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
Familiarity with Julia's Irrational typeUnderstanding of Unitful.jl conversion constantsKnowledge of arbitrary precision arithmetic
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
35
Research direction
Investigate the current definition of conversion constants in Unitful.jl, likely in src/units.jl or src/conversion.jl. Propose to replace Float64 constants with Irrational type using Base.@irrational macro, ensuring backward compatibility and maintaining performance for default use. Check for any issues with BigFloat conversions and update tests accordingly.