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The alternative to ifelse #16

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ChrisRackauckas opened this issue Jul 19, 2020 · 3 comments
Closed

The alternative to ifelse #16

ChrisRackauckas opened this issue Jul 19, 2020 · 3 comments

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@ChrisRackauckas
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ChrisRackauckas commented Jul 19, 2020 •
edited by sync-by-unito bot
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ifelse is a bit problematic for symbolic libraries because it's in Core and not in Base and dispatch cannot be added to it. So, while we want to represent branching, we need to do so without using ifelse. The opportunities are something like:

  • ModelingToolkit.ifelse
  • _ifelse (exported)
  • A different name

We need to just pick one and start using it, and whatever is chosen is what the eventual tracer should transform things to.

┆Issue is synchronized with this Trello card by Unito
@ChrisRackauckas
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JuliaLang/julia#32844 hopefully this changes in Base.

ChrisRackauckas referenced this issue in SciML/ModelingToolkit.jl Sep 2, 2020
@ChrisRackauckas
Handle conditionals and abs
341ba5e 
It's time we finally handle #531, https://github.com/SciML/ModelingToolkit.jl/issues/532, and https://discourse.julialang.org/t/differentiation-method-for-element-wise-abs-function-applied-on-operation-types-in-modelingtoolkit-jl/45867/4 . This PR creates a `ModelingToolkit.ifelse` with derivative fixes for `abs` to make it so standard conditional code can work. While tracing cannot correctly make these operations, this would at least allow directly written symbolic code to handle conditions, so we're at least as good (or bad) as TensorFlow.
@ChrisRackauckas ChrisRackauckas transferred this issue from SciML/ModelingToolkit.jl Feb 26, 2021
@ChrisRackauckas
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The solution ended up being https://github.com/SciML/IfElse.jl

@devmotion
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AFAICT this issue can be fixed since it was fixed upstream. Base.ifelse has been available since Julia 1.8.

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@devmotion @ChrisRackauckas