# Getting started with Differential Equations

**URL:** <https://discourse.julialang.org/t/getting-started-with-differential-equations/61055>\
**Category:** Modelling & Simulations\
**Tags:** question\
**Created:** [May 13, 2021, 12:31am UTC](https://discourse.julialang.org/t/getting-started-with-differential-equations/61055 "2021-05-13T00:31:11Z")\
**Posts on this page:** 8\
**Page:** 1

<div class="post-metadata">

**Author:** ![ufechner7](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/ufechner7/32/51363_2.png) [@ufechner7](https://discourse.julialang.org/u/ufechner7)\
**Post date:** [May 13, 2021, 12:31am UTC](https://discourse.julialang.org/t/getting-started-with-differential-equations/61055/1 "2021-05-13T00:31:11Z")

</div>

I am trying to port a simple example from Python to Julia, but already the first example from the Tutorial fails:

```julia
using DifferentialEquations

function lorenz(t, u, du)
    du[1] = 10.0(u[2]-u[1])
    du[2] = u[1]*(28.0-u[3]) - u[2]
    du[3] = u[1]*u[2] - (8/3)*u[3]
end

u0 = [1.0; 0.0; 0.0]
tspan = (0.0, 100.0)
prob = ODEProblem(lorenz, u0, tspan)
sol = solve(prob)

```

Output:

```julia
julia> include("src/RadauTether.jl")
ERROR: LoadError: Parameters were indexed but the parameters are `nothing`. You likely forgot to pass in parameters to the DEProblem!
Stacktrace:
  [1] error(s::String)
    @ Base ./error.jl:33
  [2] getindex(#unused#::SciMLBase.NullParameters, i::Int64)
    @ SciMLBase ~/.julia/packages/SciMLBase/XuLdB/src/problems/problem_utils.jl:140
...

```

Any idea?

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<div class="post-metadata">

**Author:** ![ufechner7](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/ufechner7/32/51363_2.png) [@ufechner7](https://discourse.julialang.org/u/ufechner7)\
**Post date:** [May 13, 2021, 12:46am UTC](https://discourse.julialang.org/t/getting-started-with-differential-equations/61055/2 "2021-05-13T00:46:48Z")

</div>

To answer myself: The example was from an outdated version of the documentation.

The latest documentation ([Ordinary Differential Equations · DifferentialEquations.jl](https://diffeq.sciml.ai/stable/tutorials/ode_example/#Example-2:-Solving-Systems-of-Equations)) is correct:

```julia
using DifferentialEquations

function lorenz!(du,u,p,t)
    du[1] = 10.0*(u[2]-u[1])
    du[2] = u[1]*(28.0-u[3]) - u[2]
    du[3] = u[1]*u[2] - (8/3)*u[3]
end

u0 = [1.0; 0.0; 0.0]
tspan = (0.0, 100.0)
prob = ODEProblem(lorenz!, u0, tspan)
sol = solve(prob)

```

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<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:** [May 13, 2021, 12:51am UTC](https://discourse.julialang.org/t/getting-started-with-differential-equations/61055/3 "2021-05-13T00:51:41Z")

</div>

Anything we can do to make the old version of the docs less likely to show up?

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<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:** [May 13, 2021, 1:04am UTC](https://discourse.julialang.org/t/getting-started-with-differential-equations/61055/4 "2021-05-13T01:04:16Z")

</div>

The old docs at least give you a big javascript popup box saying it’s the old version.

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<div class="post-metadata">

**Author:** ![ufechner7](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/ufechner7/32/51363_2.png) [@ufechner7](https://discourse.julialang.org/u/ufechner7)\
**Post date:** [May 13, 2021, 1:13am UTC](https://discourse.julialang.org/t/getting-started-with-differential-equations/61055/5 "2021-05-13T01:13:23Z")

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Well, if I google: “ordinary differential equations julia” the first hit is:  
[https://diffeq.sciml.ai/v2.0/](https://diffeq.sciml.ai/v2.0/)

And if I go to the examples I end up here:  
[https://diffeq.sciml.ai/v2.0/tutorials/ode\_example.html#Example-2:-Solving-Systems-of-Equations-1](https://diffeq.sciml.ai/v2.0/tutorials/ode_example.html#Example-2:-Solving-Systems-of-Equations-1)

And this doesn’t work. And no popup box (well, perhaps Firefox is blocking it?)

Which version is the currently stable version?

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<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:** [May 13, 2021, 1:19am UTC](https://discourse.julialang.org/t/getting-started-with-differential-equations/61055/6 "2021-05-13T01:19:31Z")

</div>

![Capture](https://global.discourse-cdn.com/julialang/original/3X/d/b/db1a2e7b06df19b5a0ed75751c837ec481c7d956.png)

You don’t get that box?

> [@ufechner7](#):
>
> Which version is the currently stable version?

v6.17

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<div class="post-metadata">

**Author:** ![ufechner7](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/ufechner7/32/51363_2.png) [@ufechner7](https://discourse.julialang.org/u/ufechner7)\
**Post date:** [May 13, 2021, 1:22am UTC](https://discourse.julialang.org/t/getting-started-with-differential-equations/61055/7 "2021-05-13T01:22:56Z")

</div>

Actually, now I also see the box. But it is in the lower right corner and I have a widescreen monitor, so I did not see it first.

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<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:** [May 13, 2021, 1:25am UTC](https://discourse.julialang.org/t/getting-started-with-differential-equations/61055/8 "2021-05-13T01:25:36Z")

</div>

@pfitzseb getting that comment again.

To be fair, it’s just a hack that @pfitzseb put into our docs to try and fix this problem. It’s a major issue with Documenter.jl and everyone should spam:

[https://github.com/JuliaDocs/Documenter.jl/issues/1449](https://github.com/JuliaDocs/Documenter.jl/issues/1449)

[https://github.com/JuliaDocs/Documenter.jl/issues/539](https://github.com/JuliaDocs/Documenter.jl/issues/539)

[https://github.com/JuliaLang/julia/issues/22936](https://github.com/JuliaLang/julia/issues/22936)

It’s now been the #1 issue with Documenter.jl for four years so, hopefully someone comes up with a built in solution.