# Trying to make my robust logistic function differentiable as part of AD, getting errors so far

**URL:** https://discourse.julialang.org/t/trying-to-make-my-robust-logistic-function-differentiable-as-part-of-ad-getting-errors-so-far/38838
**Category:** General Usage
**Tags:** question
**Created:** [May 5, 2020, 9:46pm UTC](https://discourse.julialang.org/t/trying-to-make-my-robust-logistic-function-differentiable-as-part-of-ad-getting-errors-so-far/38838 "2020-05-05T21:46:22Z")
**Posts on this page:** 1
**Showing post:** 10

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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: [May 6, 2020, 10:45am UTC](https://discourse.julialang.org/t/trying-to-make-my-robust-logistic-function-differentiable-as-part-of-ad-getting-errors-so-far/38838/10 "2020-05-06T10:45:52Z")

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Tangentially related, subnormals can be really slow to compute with ([Subnormal number - Wikipedia](https://en.wikipedia.org/wiki/Denormal_number#Performance_issues), [50x speed difference in gemv for different values in vector](https://discourse.julialang.org/t/50x-speed-difference-in-gemv-for-different-values-in-vector/2755), [Performance Tips · The Julia Language](https://docs.julialang.org/en/v1/manual/performance-tips/#Treat-Subnormal-Numbers-as-Zeros-1))

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