# Custom types in ForwardDiff
**URL:** https://discourse.julialang.org/t/custom-types-in-forwarddiff/24610
**Category:** Optimization (Mathematical)
**Tags:** jump
**Created:** [May 25, 2019, 7:15pm UTC](https://discourse.julialang.org/t/custom-types-in-forwarddiff/24610 "2019-05-25T19:15:36Z")
**Posts on this page:** 9
**Page:** 1
### Author:  [@tamasgal](https://discourse.julialang.org/u/tamasgal)
#### Post date: [May 25, 2019, 7:15pm UTC](https://discourse.julialang.org/t/custom-types-in-forwarddiff/24610/1 "2019-05-25T19:15:36Z")
This might be trivial but I am currently fighting with `JuMP` to accept my quality function for the minimisation procedure. I figured out that my custom type:
```julia
struct Position <: FieldVector{3, Float64}
x::Float64
y::Float64
z::Float64
end
```
is causing this error:
```julia
MethodError: no method matching Float64(::ForwardDiff.Dual{ForwardDiff.Tag{getfield(JuMP, Symbol("##84#86")){KM3NeT.MultiDUMinimiser},Float64},Float64,6})
Closest candidates are:
Float64(::Real, !Matched::RoundingMode) where T<:AbstractFloat at rounding.jl:194
Float64(::T<:Number) where T<:Number at boot.jl:741
Float64(!Matched::Int8) at float.jl:60
```
when I try to
```julia
register(model, :qfunc, 6, m, autodiff=true)
...
...
...
@NLobjective(model, Min, qfunc(x, y, z, ฮธ, ฯ, tโ))
optimize!(model) # this is the line which fails with the message above
```
Given the candidates, I guess I have to somehow implement something related to roundings ๐ ? Can someone toss me in the right direction?
I found this discussion but still clueless: [https://github.com/JuliaDiffEq/DiffEqBase.jl/issues/169](https://github.com/JuliaDiffEq/DiffEqBase.jl/issues/169)
---
### Author:  [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)
#### Post date: [May 25, 2019, 7:16pm UTC](https://discourse.julialang.org/t/custom-types-in-forwarddiff/24610/2 "2019-05-25T19:16:40Z")
```julia
struct Position{T} <: FieldVector{3, T}
x::T
y::T
z::T
end
```
---
### Author:  [@tamasgal](https://discourse.julialang.org/u/tamasgal)
#### Post date: [May 25, 2019, 7:29pm UTC](https://discourse.julialang.org/t/custom-types-in-forwarddiff/24610/3 "2019-05-25T19:29:38Z")
Thanks Chris, I tried it but I still get the same error ๐
---
### Author:  [@tamasgal](https://discourse.julialang.org/u/tamasgal)
#### Post date: [May 25, 2019, 7:34pm UTC](https://discourse.julialang.org/t/custom-types-in-forwarddiff/24610/4 "2019-05-25T19:34:44Z")
I just checked, I think itโs caused by this type now (the `Position` stuff works, and I also added it to `Direction`):
```julia
struct Track
dir::Direction
pos::Position
time::Float64
end
```
Iโll now try to parametrise that with
```julia
2 struct Track{T}
1 dir::Direction{T}
89 pos::Position{T}
1 time::T
2 end
```
---
### Author:  [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)
#### Post date: [May 25, 2019, 7:35pm UTC](https://discourse.julialang.org/t/custom-types-in-forwarddiff/24610/5 "2019-05-25T19:35:58Z")
Any place where you write `Float64`, replace it with a parameterization.
---
### Author:  [@tamasgal](https://discourse.julialang.org/u/tamasgal)
#### Post date: [May 25, 2019, 7:36pm UTC](https://discourse.julialang.org/t/custom-types-in-forwarddiff/24610/6 "2019-05-25T19:36:58Z")
Makes sense now, thanks ๐
---
### Author:  [@tamasgal](https://discourse.julialang.org/u/tamasgal)
#### Post date: [May 25, 2019, 7:41pm UTC](https://discourse.julialang.org/t/custom-types-in-forwarddiff/24610/7 "2019-05-25T19:41:29Z")
The problem is, now I destroyed some other calls, namely when I create a track using a standard vector:
```julia
MethodError: no method matching KM3NeT.Track(::Array{Float64,1}, ::Array{Float64,1}, ::Float64)
Closest candidates are:
KM3NeT.Track(!Matched::Direction{T}, !Matched::Position{T}, ::T) where T at /home/tgal/.julia/dev/KM3NeT/src/types.jl:88
```
I am now lost in parametric hellโฆ
---
### Author:  [@tamasgal](https://discourse.julialang.org/u/tamasgal)
#### Post date: [May 25, 2019, 7:49pm UTC](https://discourse.julialang.org/t/custom-types-in-forwarddiff/24610/8 "2019-05-25T19:49:29Z")
OK, this one works ๐
```julia
struct Track
dir::Direction
pos::Position
time
end
```
---
### Author:  [@jlperla](https://discourse.julialang.org/u/jlperla)
#### Post date: [May 25, 2019, 9:06pm UTC](https://discourse.julialang.org/t/custom-types-in-forwarddiff/24610/9 "2019-05-25T21:06:21Z")
Frequently you need to make the types parametric and allow different types between the fields (ie, you only want dual numbers in one of them).