# What does "user\_cache: method has not been implemented for the integrator" mean?

**URL:** <https://discourse.julialang.org/t/what-does-user-cache-method-has-not-been-implemented-for-the-integrator-mean/19233>\
**Category:** New to Julia\
**Tags:** diffeq, error\
**Created:** [January 3, 2019, 2:30pm UTC](https://discourse.julialang.org/t/what-does-user-cache-method-has-not-been-implemented-for-the-integrator-mean/19233 "2019-01-03T14:30:05Z")\
**Posts on this page:** 1\
**Showing post:** 3

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**Author:** ![asprionj](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/asprionj/32/6856_2.png) [@asprionj](https://discourse.julialang.org/u/asprionj)\
**Post date:** [April 13, 2020, 10:31pm UTC](https://discourse.julialang.org/t/what-does-user-cache-method-has-not-been-implemented-for-the-integrator-mean/19233/3 "2020-04-13T22:31:41Z")

</div>

There’s problems with that approach, though. First, when using `autodiff`, the type constraint on the “user-defined” fields of the data do not match, i.e. only one of the fields is a dual at a time. So, using e.g. `Trapezoid()` instead of `Tsit5` as solver, I get the error:

```julia
MethodError: no method matching SimType(::Array{ForwardDiff.Dual{ForwardDiff.Tag{DiffEqBase.UJacobianWrapper{ODEFunction{true,typeof(f),LinearAlgebra.UniformScaling{Bool},Nothing,Nothing,Nothing,Nothing,Nothing,Nothing,Nothing,Nothing,Nothing,Nothing,Nothing},Float64,DiffEqBase.NullParameters},Float64}(),Float64,2},1}, ::Float64)
Closest candidates are:
  SimType(::Array{T,1}, !Matched::T) where T ... 

```

I remember there is a way of solving this, I read it somewhere some time ago. But, IMO, that’s rather complicated for a “standard user”. Is there any better way?

Ok, so let’s turn off `autodiff` by using `Trapezoid(autodiff=false)`. I then get:

```julia
MethodError: no method matching SimType(::Array{Float64,2}, ::Float64)
Closest candidates are:
  SimType(!Matched::Array{T,1}, ::T) where T ... 

```

So, somehow, this (and many other solvers) try to initialise a 2D array…?

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