# Bent identity activation function and Flux.jl?

**URL:** https://discourse.julialang.org/t/bent-identity-activation-function-and-flux-jl/31807
**Category:** Machine Learning
**Created:** [December 3, 2019, 2:37pm UTC](https://discourse.julialang.org/t/bent-identity-activation-function-and-flux-jl/31807 "2019-12-03T14:37:07Z")
**Posts on this page:** 3
**Page:** 1

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### Author: ![bienpierre](https://avatars.discourse-cdn.com/v4/letter/b/8c91f0/32.png) [@bienpierre](https://discourse.julialang.org/u/bienpierre)
#### Post date: [December 3, 2019, 2:37pm UTC](https://discourse.julialang.org/t/bent-identity-activation-function-and-flux-jl/31807/1 "2019-12-03T14:37:07Z")

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Dear all,  
Does flux.jl has the [bent identity](https://en.wikipedia.org/wiki/Activation_function) activation function? I don’t see it in [NNlib.jl](https://github.com/FluxML/NNlib.jl).  
Warmest regards

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### Author: ![kristoffer.carlsson](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kristoffer.carlsson/32/22_2.png) [@kristoffer.carlsson](https://discourse.julialang.org/u/kristoffer.carlsson)
#### Post date: [December 3, 2019, 4:25pm UTC](https://discourse.julialang.org/t/bent-identity-activation-function-and-flux-jl/31807/2 "2019-12-03T16:25:38Z")

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Maybe I am mistaken but isn’t it just to define

```julia
bent(x) = (√(x^2+1) - 1)/2 + x

```

and then you are done?

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<div class="post-metadata">

### Author: ![bienpierre](https://avatars.discourse-cdn.com/v4/letter/b/8c91f0/32.png) [@bienpierre](https://discourse.julialang.org/u/bienpierre)
#### Post date: [December 3, 2019, 4:58pm UTC](https://discourse.julialang.org/t/bent-identity-activation-function-and-flux-jl/31807/3 "2019-12-03T16:58:56Z")

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Thanks Mister Carlsson, it works.  
Regards