# Error doing Implicit Derivatives in ModelToolkit I think it's trying to divide by 0

**URL:** <https://discourse.julialang.org/t/error-doing-implicit-derivatives-in-modeltoolkit-i-think-its-trying-to-divide-by-0/50240>\
**Category:** General Usage\
**Tags:** question, plotting, calculus, modelingtoolkit\
**Created:** [November 16, 2020, 6:28pm UTC](https://discourse.julialang.org/t/error-doing-implicit-derivatives-in-modeltoolkit-i-think-its-trying-to-divide-by-0/50240 "2020-11-16T18:28:28Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![brett\_knoss](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/brett_knoss/32/13050_2.png) [@brett\_knoss](https://discourse.julialang.org/u/brett_knoss)\
**Post date:** [November 16, 2020, 6:28pm UTC](https://discourse.julialang.org/t/error-doing-implicit-derivatives-in-modeltoolkit-i-think-its-trying-to-divide-by-0/50240/1 "2020-11-16T18:28:29Z")

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when I try to run

```julia
 let ex = Differential(x)(f(x, y))
           func_ex = build_function(expand_derivatives(ex), x, y)
           @eval ∂xf(x, y) = ($func_ex)(x,y)
       end

```

I get an error

```julia
ERROR: type Int64 has no field value

```

I think it’s trying to find the deivative of x=0,y=0 which is not part of the

---

<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:** [November 16, 2020, 7:15pm UTC](https://discourse.julialang.org/t/error-doing-implicit-derivatives-in-modeltoolkit-i-think-its-trying-to-divide-by-0/50240/2 "2020-11-16T19:15:15Z")

</div>

0.0?

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<div class="post-metadata">

**Author:** ![brett\_knoss](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/brett_knoss/32/13050_2.png) [@brett\_knoss](https://discourse.julialang.org/u/brett_knoss)\
**Post date:** [November 16, 2020, 7:22pm UTC](https://discourse.julialang.org/t/error-doing-implicit-derivatives-in-modeltoolkit-i-think-its-trying-to-divide-by-0/50240/3 "2020-11-16T19:22:40Z")

</div>

```julia
f(x,y)=((x^2+y^2)^4)/(x^2*y)

let ex = Differential(x)(f(x, y))
           func_ex = build_function(expand_derivatives(ex), x, y)
           @eval ∂xf(x, y) = ($func_ex)(x,y)
       end

```

sorry, my bad.