# DifferentialEquations.jl ERROR: UndefVarError: CostVData not defined
**URL:** https://discourse.julialang.org/t/differentialequations-jl-error-undefvarerror-costvdata-not-defined/35939
**Category:** New to Julia
**Tags:** question, diffeq, optim
**Created:** [March 13, 2020, 5:18pm UTC](https://discourse.julialang.org/t/differentialequations-jl-error-undefvarerror-costvdata-not-defined/35939 "2020-03-13T17:18:42Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@PharmCat](https://discourse.julialang.org/u/PharmCat)
#### Post date: [March 13, 2020, 5:18pm UTC](https://discourse.julialang.org/t/differentialequations-jl-error-undefvarerror-costvdata-not-defined/35939/1 "2020-03-13T17:18:42Z")
I try to otimize function with DifferentialEquations.jl + Optim.jl like in documetation, but I have:
ERROR: UndefVarError: CostVData not defined
```julia
using DifferentialEquations, Plots, Optim, LossFunctions, Random, DiffEqParamEstim, Distributions
function pkf1!(du,u,p,t)
du[1] = - p[1] * u[1]
du[2] = p[1] * u[1] - p[2] * u[2]
end
u0 = [3.0, 0.0]
p = [0.2, 0.15]
tspan = (0.0, 50.0)
prob = ODEProblem(pkf1!,u0,tspan, p)
sol = solve(prob)
plot(sol,vars=(1))
plot!(sol,vars=(2))
x = float.(collect(0:1:50))
y = hcat(sol.(x)...)'[:,2] .* exp.(rand(Normal(), length(x)) ./ 8)
plot!(x,y)
#lossfcn = L2Loss(x,y; weight=nothing)
lossfcn = CostVData(t,data;loss_func = L2Loss, weight=nothing)
cost_function = build_loss_objective(prob, Tsit5(), lossfcn)
result = optimize(cost_function, [0.4, 0.01])
```
when i use:
```julia
lossfcn = L2Loss(x,y; weight=nothing)
```
ERROR: MethodError: no method matching L2Loss(::Array{Float64,1}, ::Array{Float64,1}; weight=nothing)
it’s not working too, but works for:
```julia
lossfcn = L2Loss(x,y)
```
what package including CostVData?
---
### Author:  [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)
#### Post date: [March 13, 2020, 6:22pm UTC](https://discourse.julialang.org/t/differentialequations-jl-error-undefvarerror-costvdata-not-defined/35939/2 "2020-03-13T18:22:37Z")
Are you looking at very old documentation? I don’t think this is mentioned at all in the last 3 years.
---
### Author:  [@PharmCat](https://discourse.julialang.org/u/PharmCat)
#### Post date: [March 15, 2020, 1:52pm UTC](https://discourse.julialang.org/t/differentialequations-jl-error-undefvarerror-costvdata-not-defined/35939/3 "2020-03-15T13:52:30Z")
I just followed by google to this: [https://docs.juliadiffeq.org/v1.9/analysis/parameter\_estimation.html](https://docs.juliadiffeq.org/v1.9/analysis/parameter_estimation.html)
so, ok, it’s not supported anymore…
---
### Author:  [@Sukera](https://discourse.julialang.org/u/Sukera)
#### Post date: [March 15, 2020, 3:11pm UTC](https://discourse.julialang.org/t/differentialequations-jl-error-undefvarerror-costvdata-not-defined/35939/4 "2020-03-15T15:11:54Z")
The current version of the docs can be found [here](https://docs.juliadiffeq.org/dev/analysis/parameter_estimation/).
---
### Author:  [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)
#### Post date: [March 15, 2020, 3:44pm UTC](https://discourse.julialang.org/t/differentialequations-jl-error-undefvarerror-costvdata-not-defined/35939/5 "2020-03-15T15:44:32Z")
> [@PharmCat](#):
>
> I just followed by google to this: [https://docs.juliadiffeq.org/v1.9/analysis/parameter\_estimation.html](https://docs.juliadiffeq.org/v1.9/analysis/parameter_estimation.html)
It says version 1.9. DifferentialEquations is on version 6.11, so yeah, it is about 3 years old documentation 🙂. I would recommend double checking version numbers if something odd is occurring: I am not sure why Google serves the old versions sometimes.
---
### Author:  [@PharmCat](https://discourse.julialang.org/u/PharmCat)
#### Post date: [March 16, 2020, 9:18pm UTC](https://discourse.julialang.org/t/differentialequations-jl-error-undefvarerror-costvdata-not-defined/35939/6 "2020-03-16T21:18:38Z")
Yep 🙂 when you said, I looked at version in link. But when I followed the google and version is not metioned at page, and I didn’t pay attantion to link. I resolved all my questons in actual documentation. Thank you! It was wery suprpriset to try use old documentation with actual package 🙂