# SimpleATsit5?

**URL:** https://discourse.julialang.org/t/simpleatsit5/90318
**Category:** General Usage
**Tags:** differentialequation
**Created:** [November 15, 2022, 10:15pm UTC](https://discourse.julialang.org/t/simpleatsit5/90318 "2022-11-15T22:15:34Z")
**Posts on this page:** 3
**Page:** 1

<div class="post-metadata">

### Author: ![PeterSimon](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/petersimon/32/25193_2.png) [@PeterSimon](https://discourse.julialang.org/u/PeterSimon)
#### Post date: [November 15, 2022, 10:15pm UTC](https://discourse.julialang.org/t/simpleatsit5/90318/1 "2022-11-15T22:15:34Z")

</div>

I’m just getting started with the `DifferentialEquations` universe. In the first paragraph after [this heading](https://diffeq.sciml.ai/stable/solvers/ode_solve/#Non-Stiff-Problems) in the documentation, it is stated that `SimpleATsit5` is a fast, viable solver for small, non-stiff ODEs. I have a simple 2 \times 2 BVP so I would like to try it as a possible faster alternative to `Tsit5`. But when I try to use it e.g. in

```julia
solve(bvp, Shooting(SimpleATsit5()))

```

I get

```julia
UndefVarError: SimpleATsit5 not defined

```

Is there another way to access it?

---

<div class="post-metadata">

### Author: ![Oscar\_Smith](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/oscar_smith/32/25343_2.png) [@Oscar\_Smith](https://discourse.julialang.org/u/Oscar_Smith)
#### Post date: [November 15, 2022, 10:45pm UTC](https://discourse.julialang.org/t/simpleatsit5/90318/2 "2022-11-15T22:45:31Z")

</div>

They are defined in [GitHub - SciML/SimpleDiffEq.jl: Simple differential equation solvers in native Julia for scientific machine learning (SciML)](https://github.com/SciML/SimpleDiffEq.jl). The docs should arguably be updated.

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<div class="post-metadata">

### Author: ![PeterSimon](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/petersimon/32/25193_2.png) [@PeterSimon](https://discourse.julialang.org/u/PeterSimon)
#### Post date: [November 15, 2022, 11:27pm UTC](https://discourse.julialang.org/t/simpleatsit5/90318/3 "2022-11-15T23:27:25Z")

</div>

Thanks! `using SimpleDiffEq` did the trick. Surprisingly, `SimpleATsit5` is 10 times slower for my problem than `Tsit5`. In any case, I submitted a [PR](https://github.com/SciML/DiffEqDocs.jl/pull/599) to the documentation showing how to access `SimpleATsit5`.