# How to make a vector of observables in GLMakie
**URL:** https://discourse.julialang.org/t/how-to-make-a-vector-of-observables-in-glmakie/111012
**Category:** Modelling & Simulations
**Tags:** question
**Created:** [March 1, 2024, 1:06pm UTC](https://discourse.julialang.org/t/how-to-make-a-vector-of-observables-in-glmakie/111012 "2024-03-01T13:06:37Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@Luigi\_Marongiu](https://discourse.julialang.org/u/Luigi_Marongiu)
#### Post date: [March 1, 2024, 1:06pm UTC](https://discourse.julialang.org/t/how-to-make-a-vector-of-observables-in-glmakie/111012/1 "2024-03-01T13:06:38Z")
I am trying to make an interactive plot of a SIV model using GLMakie. I have created the parameters as observable. I now need to make the parameters to pass to the solver. One is `u0` that stores the initial values of the variables. I used to instantiate u0 as a vector/array with vcat. How do I do the same with an observable? I tried with @lift but I got an error:
```julia
julia> s0 = 1e5 # default starting amount of naive bacteria
100000.0
julia> i0 = 0 # default starting amount of infected bacteria
0
julia> v0 = 1e5 # default starting amount of phages
100000.0
julia> S0 = Observable(s0)
Observable(100000.0)
julia> I0 = Observable(i0)
Observable(0)
julia> V0 = Observable(v0)
Observable(100000.0)
julia> u0 = vcat(S0, I0, V0)
3-element Vector{Observable}:
Observable(100000.0)
Observable(0)
Observable(100000.0)
julia> U0 = @lift(vcat(S0, I0, V0))
ERROR: Did not find any interpolated observables. Use '$(observable)' to interpolate it into the macro.
Stacktrace:
[1] error(s::String)
@ Base ./error.jl:35
[2] var"@lift"( __source__ ::LineNumberNode, __module__ ::Module, exp::Any)
@ Makie ~/.julia/packages/Makie/VRavR/src/interaction/liftmacro.jl:77
[3] eval
@ ./boot.jl:385 [inlined]
[4] eval
@ ./Base.jl:88 [inlined]
[5] repleval(m::Module, code::Expr, ::String)
@ VSCodeServer ~/.vscode/extensions/julialang.language-julia-1.73.2/scripts/packages/VSCodeServer/src/repl.jl:229
[6] (::VSCodeServer.var"#110#112"{Module, Expr, REPL.LineEditREPL, REPL.LineEdit.Prompt})()
@ VSCodeServer ~/.vscode/extensions/julialang.language-julia-1.73.2/scripts/packages/VSCodeServer/src/repl.jl:192
[7] with_logstate(f::Function, logstate::Any)
@ Base.CoreLogging ./logging.jl:515
[8] with_logger
@ ./logging.jl:627 [inlined]
[9] (::VSCodeServer.var"#109#111"{Module, Expr, REPL.LineEditREPL, REPL.LineEdit.Prompt})()
@ VSCodeServer ~/.vscode/extensions/julialang.language-julia-1.73.2/scripts/packages/VSCodeServer/src/repl.jl:193
[10] #invokelatest#2
@ ./essentials.jl:892 [inlined]
[11] invokelatest(::Any)
@ Base ./essentials.jl:889
[12] (::VSCodeServer.var"#62#63")()
@ VSCodeServer ~/.vscode/extensions/julialang.language-julia-1.73.2/scripts/packages/VSCodeServer/src/eval.jl:34
julia> U0 = $(vcat(S0, I0, V0))
ERROR: syntax: "$" expression outside quote around REPL[23]:1
Stacktrace:
[1] top-level scope
@ REPL[23]:1
julia> U0 = '$(vcat(S0, I0, V0))'
ERROR: ParseError:
# Error @ REPL[24]:1:7
U0 = '$(vcat(S0, I0, V0))'
# └─────────────────┘ ── character literal contains multiple characters
Stacktrace:
[1] top-level scope
@ none:1
```
How can I set vectors of observables for ODE solved with `DifferentialEquations`?
---
### Author:  [@tomaklutfu](https://discourse.julialang.org/u/tomaklutfu)
#### Post date: [March 1, 2024, 1:21pm UTC](https://discourse.julialang.org/t/how-to-make-a-vector-of-observables-in-glmakie/111012/2 "2024-03-01T13:21:25Z")
I don’t think you can directly use a vector of `Observable`’s as states in `DifferentialEquations` but you can use an `Observable` of a vector with `lift`.
> [@Luigi\_Marongiu](#):
>
> ```julia
> julia> U0 = @lift(vcat(S0, I0, V0))
> ERROR: Did not find any interpolated observables. Use '$(observable)' to interpolate it into the macro.
>
> ```
Error also explains what the solution might be. Interpolation in this context means a `julia` syntactical sugar for replacing by value in `julia` expression ref: [Metaprogramming · The Julia Language](https://docs.julialang.org/en/v1/manual/metaprogramming/#man-expression-interpolation)
```julia
julia> U0 = @lift(vcat($S0, $I0, $V0))
Observable([100000.0, 0.0, 100000.0])
```
For using in conjunction with `DifferentialEquations`, you can look at ref: [Observables & Interaction · Makie](https://docs.makie.org/stable/explanations/nodes/#chaining_observables_with_lift)
---
### Author:  [@Luigi\_Marongiu](https://discourse.julialang.org/u/Luigi_Marongiu)
#### Post date: [March 1, 2024, 2:22pm UTC](https://discourse.julialang.org/t/how-to-make-a-vector-of-observables-in-glmakie/111012/3 "2024-03-01T14:22:00Z")
> [@tomaklutfu](#):
>
> `U0 = @lift(vcat($S0, $I0, $V0))`
Thanks!