# Right way to "static" allocate vectors in a function

**URL:** <https://discourse.julialang.org/t/right-way-to-static-allocate-vectors-in-a-function/18469>\
**Category:** Performance\
**Created:** [December 8, 2018, 8:00pm UTC](https://discourse.julialang.org/t/right-way-to-static-allocate-vectors-in-a-function/18469 "2018-12-08T20:00:16Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Ronis\_BR](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/ronis_br/32/50999_2.png) [@Ronis\_BR](https://discourse.julialang.org/u/Ronis_BR)\
**Post date:** [December 8, 2018, 8:00pm UTC](https://discourse.julialang.org/t/right-way-to-static-allocate-vectors-in-a-function/18469/1 "2018-12-08T20:00:16Z")

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Hi guys!

I have some functions that were called to fill a 2000 x 2000 matrix. Some functions need to allocate 2000x1 vectors to do the computations. However, those functions are called like 2000x2000 times 😅 Something like:

```julia
function func1(...)
    den_ar = Vector{Float64}(undef,M)
    int_fe = Vector{Float64}(undef,M)
    ablacao_fe = Vector{Float64}(undef,M)
    ...

```

The problem is that the allocations are very, very high. My measurements are showing 145 GB in allocations. The execution time is 135s vs. 46s in FORTRAN.

In C, this is solved by making those vectors static. I read some posts here and even a discussion in GitHub about a static variable in a Julia function. However, I was not be able to find what is the best approach to it.

Can anyone help me please?

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**Author:** ![rdeits](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/rdeits/32/286_2.png) [@rdeits](https://discourse.julialang.org/u/rdeits)\
**Post date:** [December 8, 2018, 8:17pm UTC](https://discourse.julialang.org/t/right-way-to-static-allocate-vectors-in-a-function/18469/2 "2018-12-08T20:17:06Z")

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First of all, I’d suggest not doing this at all. Instead, create a `Func1Workspace` type (or whatever you want to call it) which holds those vectors. Then change your method to something like:

```julia
function func1!(work::Func1Workspace, ...)
  ...
end

```

You can even make a convenient definition that constructs a workspace (for situations where convenience is more important than performance):

```julia
function func1(...)
  work = Func1Workspace()
  func1!(work, ...)
end

```

In this way, you gain a number of benefits:

1. Your code is safe for parallel execution (while the static approach definitely is not)
2. It’s easy to handle workspaces with different sizes, which the static approach can’t easily do.
3. It’s very obvious what is going on and when allocation is happening, which makes things easy for users of your code to understand

That said, if you really want static variables, you can use a `let` block and an anonymous function:

```julia
julia> const foo = let x = zeros(100)
         function (y)
           x .= y
           x
         end
       end
#3 (generic function with 1 method)

julia> foo(1)
100-element Array{Float64,1}:
 1.0
 1.0
 1.0
 1.0
 1.0
 1.0
 1.0
 1.0
 1.0
 1.0
 1.0
 1.0
 ⋮  
 1.0
 1.0
 1.0
 1.0
 1.0
 1.0
 1.0
 1.0
 1.0
 1.0
 1.0
 1.0

julia> @allocated foo(2)
0

```

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<div class="post-metadata">

**Author:** ![Ronis\_BR](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/ronis_br/32/50999_2.png) [@Ronis\_BR](https://discourse.julialang.org/u/Ronis_BR)\
**Post date:** [December 8, 2018, 8:18pm UTC](https://discourse.julialang.org/t/right-way-to-static-allocate-vectors-in-a-function/18469/3 "2018-12-08T20:18:47Z")

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Thanks @rdeits ! I will go with the workspace approach. Seems way cleaner.