# FastDense, FastChain

**URL:** <https://discourse.julialang.org/t/fastdense-fastchain/98210>\
**Category:** General Usage\
**Created:** [May 2, 2023, 4:28pm UTC](https://discourse.julialang.org/t/fastdense-fastchain/98210 "2023-05-02T16:28:57Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![erlebach](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/erlebach/32/12973_2.png) [@erlebach](https://discourse.julialang.org/u/erlebach)\
**Post date:** [May 2, 2023, 4:28pm UTC](https://discourse.julialang.org/t/fastdense-fastchain/98210/1 "2023-05-02T16:28:58Z")

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Which package contains FastChain and FastDense? I am using Julia 1.9.rc1. Even though I loaded `DiffEqFlux`n and `Flux`, `FastChain` and `FastDense` are not found. Any insight is appreciated. Thanks.

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**Author:** ![ChrisRackauckas](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/chrisrackauckas/32/77_2.png) [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)\
**Post date:** [May 2, 2023, 4:55pm UTC](https://discourse.julialang.org/t/fastdense-fastchain/98210/2 "2023-05-02T16:55:29Z")

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Those were deprecated in 2021. You should’ve been getting deprecation messages for awhile now. Feel free to continue using the older DiffEqFlux v1.x releases if you need it, but we highly recommend updating to Lux (as the deprecation messages have said). Lux is essentially the successor to FastChain which took the explicit chain syntax concept and made it into a fully complete machine learning library:

[https://lux.csail.mit.edu/stable/](https://lux.csail.mit.edu/stable/)

Since that exists these days, there really is no reason for FastDense and so all of the docs were changed out to use Lux over 2022 while we kept the deprecation message.

DiffEqFlux dropped them in the v2 update, which you will only get if you manually bump the major, so please test when bumping major versions (a standard practice)

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**Author:** ![erlebach](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/erlebach/32/12973_2.png) [@erlebach](https://discourse.julialang.org/u/erlebach)\
**Post date:** [May 2, 2023, 5:17pm UTC](https://discourse.julialang.org/t/fastdense-fastchain/98210/3 "2023-05-02T17:17:49Z")

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Got it, thanks. I have transitioned to Lux, but this was an older code. I do t recall deprecated messages. On the other hand, I don’t use Julia on a regular basis.

Gordon

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<div class="post-metadata">

**Author:** ![ChrisRackauckas](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/chrisrackauckas/32/77_2.png) [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)\
**Post date:** [May 2, 2023, 5:24pm UTC](https://discourse.julialang.org/t/fastdense-fastchain/98210/4 "2023-05-02T17:24:06Z")

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I’d recommend using the same manifest on older code to get the same package versions, or at least a Project.toml to get the same major versions.

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**Author:** ![erlebach](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/erlebach/32/12973_2.png) [@erlebach](https://discourse.julialang.org/u/erlebach)\
**Post date:** [May 2, 2023, 5:29pm UTC](https://discourse.julialang.org/t/fastdense-fastchain/98210/5 "2023-05-02T17:29:13Z")

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Thanks. Good suggestion. The problem is that I upgraded my project.toml to Julia 9.x, which led to the issues.