# Strange behavior of differentiating constant functions in Zygote

**URL:** https://discourse.julialang.org/t/strange-behavior-of-differentiating-constant-functions-in-zygote/32593
**Category:** New to Julia
**Created:** [December 23, 2019, 12:39am UTC](https://discourse.julialang.org/t/strange-behavior-of-differentiating-constant-functions-in-zygote/32593 "2019-12-23T00:39:10Z")
**Posts on this page:** 2
**Page:** 1

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### Author: ![yuxi.liu](https://avatars.discourse-cdn.com/v4/letter/y/839c29/32.png) [@yuxi.liu](https://discourse.julialang.org/u/yuxi.liu)
#### Post date: [December 23, 2019, 12:39am UTC](https://discourse.julialang.org/t/strange-behavior-of-differentiating-constant-functions-in-zygote/32593/1 "2019-12-23T00:39:10Z")

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Why is

```julia
using Zygote: gradient
gradient((x -> 0.0), 1)

```

giving  
`(nothing, )`  
?

---

<div class="post-metadata">

### Author: ![baggepinnen](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/baggepinnen/32/693_2.png) [@baggepinnen](https://discourse.julialang.org/u/baggepinnen)
#### Post date: [December 23, 2019, 12:40am UTC](https://discourse.julialang.org/t/strange-behavior-of-differentiating-constant-functions-in-zygote/32593/2 "2019-12-23T00:40:49Z")

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Nothing encodes zero derivative in zygote. This is chosen so that some computations can be avoided in more complex code.