# Dynamic dimensions of optimization variable in JuMP
**URL:** https://discourse.julialang.org/t/dynamic-dimensions-of-optimization-variable-in-jump/24399
**Category:** Optimization (Mathematical)
**Tags:** metaprogramming
**Created:** [May 20, 2019, 12:19pm UTC](https://discourse.julialang.org/t/dynamic-dimensions-of-optimization-variable-in-jump/24399 "2019-05-20T12:19:53Z")
**Posts on this page:** 2
**Page:** 1
### Author:  [@lgo](https://discourse.julialang.org/u/lgo)
#### Post date: [May 20, 2019, 12:19pm UTC](https://discourse.julialang.org/t/dynamic-dimensions-of-optimization-variable-in-jump/24399/1 "2019-05-20T12:19:53Z")
Hello,
Although my question itself is JuMP related, the underlying problem relates to metaprogramming in general:
As the title suggests, I want to create a variable, which dimensions change depending on the numeric input provided. Preferably, this should be archived within the @variable macro. So far, I just write a uniform value into a dimension that was found to be non-existent. The performance gains from completely omitting these dimensions are not significant, but it would allow to greatly facilitate further parts of my code.
I have managed to introduce a new keyword argument “set\_in” to the @variable macro that is expression of all relevant dimensions and filters the first input expression at the beginning of my new macro. Accordingly, the macro below will omit dimension i from the created variable.
> using JuMP
>
> m = Model()
>
> VarDim\_dic = Dict(:a =\> 1:8, :b =\> `[]`)
>
> @variable\_new(m, x[a= VarDim\_dic[:a], b= VarDim\_dic[:b]], set\_in = `:(` (a ) ) )
>
> macro variable\_new(args…)
>
> …
>
> extra, kw\_args, requestedcontainer = \_extract\_kw\_args(args[2:end])
>
> extra = filterUsedSets(extra,set\_in)
>
> …
However, this obviously won’t work, if set\_in is not a hard-coded, but generated dynamically as desired:
> RelSets = Meta.parse(join(filter(x → !isempty(VarDim\_dic`[x]`),collect(keys(VarDim\_dic))),", "))
>
> @variable\_new(m, x[a= VarDim\_dic[:a],b= VarDim\_dic][:b], set\_in = RelSets )
I tried to add the filtering to the code being actually written by the macro as an expression, but did not succeed. So, first of all I would like to know, if what I’m trying to achieve is even possible and second, if I’ve there is a smarter way to this (For exampe, I thought about generating nested if clauses as well). I think, only if this is the case, it makes sense to have a closer look at my current code in detail. Thanks!
---
### Author:  [@odow](https://discourse.julialang.org/u/odow)
#### Post date: [May 20, 2019, 1:22pm UTC](https://discourse.julialang.org/t/dynamic-dimensions-of-optimization-variable-in-jump/24399/2 "2019-05-20T13:22:29Z")
Most probably, you want something simpler like
```nohighlight
function create_indices(i)
return [(1, i), (2, i), (:a, "c")]
end
indices = create_indices(1)
model = Model()
@variable(model, x[indices])
# output
1-dimensional DenseAxisArray{VariableRef,1,...} with index sets:
Dimension 1, Tuple{Any,Any}[(1, 1), (2, 1), (:a, "c")]
And data, a 3-element Array{VariableRef,1}:
x[(1, 1)]
x[(2, 1)]
x[(:a, "c")]
```
The `create_indices` function could produce indices of the right dimension based on an argument.