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UnitfulChainRules.jl

UnitfulChainRules.jl adds support for differentiating through scalar Unitful.Quantity construction and arithmetic. The arithmetic rules are drawn from the existing ChainRules.jl scalar rules, so this package provides the Quantity autodiff rules and utilities.

Right now, this includes rrule, frule implementations for the Quantity construction and the ProjectTo utility. We implement projection onto Quantitys and projection of Quantitys onto Real, Complex numbers.

Usage

To import the rules, all that is required is importing UnitfulChainRules.jl in addition to Unitful.jl.

using Unitful: W, μm, ms
using UnitfulChainRules
using Zygote

Zygote.gradient((x,y) -> (x*W)/(y*μm)/ms, 3.0*W, 2.0*μm)
# (0.5 W μm^-2 ms^-1, -0.75 W^2 μm^-3 ms^-1)

Zygote.gradient((x,y) -> (x*ms + 9*y*ms)/μm, 2.0*W, 3.0*W)
# (1.0 ms μm^-1, 9.0 ms μm^-1)

Array Rules

This package does not yet include compatibility for operations between arrays of Unitful.Quantitys, like most LinearAlgebra ops. An issue is open for discussing how to best add array rules.

Related Packages

• Unitful.jl - Implements dimensional numerical quantities for Julia
• ChainRules.jl - Provides a standard set of rules for interfacing with various autodiff backends in Julia