# Work around for Meshgrid of python into julia

**URL:** <https://discourse.julialang.org/t/work-around-for-meshgrid-of-python-into-julia/97807>\
**Category:** New to Julia\
**Tags:** question, arrays, physics\
**Created:** [April 23, 2023, 6:15am UTC](https://discourse.julialang.org/t/work-around-for-meshgrid-of-python-into-julia/97807 "2023-04-23T06:15:20Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![aburousan](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/aburousan/32/28525_2.png) [@aburousan](https://discourse.julialang.org/u/aburousan)\
**Post date:** [April 23, 2023, 6:15am UTC](https://discourse.julialang.org/t/work-around-for-meshgrid-of-python-into-julia/97807/1 "2023-04-23T06:15:20Z")

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I am trying to plot a potential diagram for two charge plates. I have a code which does that in python. I am now trying to convert that code block into julia. But I am unable to do so. Can someone help?  
The code in python :

 ![IMG_20230423_113042](https://global.discourse-cdn.com/julialang/original/3X/f/f/ff23dc7bd4062c9e2ed214806cde83640564b386.jpeg)  
The code I have written in julia :

```plaintext
N = 100
grids = zeros(N,N,N) .+ 0.5
grids[30:70,30:70, 20] .= 1
grids[30:70,30:70, 80] .= 0
mask_pos = grids .== 1
mask_nev = grids .== 0
heatmap(mask_pos[:,:,20])
xv = yv = zv = collect(1:N)
grids = 1 .- (zv /100)
contour(grids[0,:,:])

```

But this is showing a error :

```julia
BoundsError: attempt to access 100-element Vector{Float64} at index [0, 1:1, 1:1]
Stacktrace:
 [1] throw_boundserror(A::Vector{Float64}, I::Tuple{Int64, Base.Slice{Base.OneTo{Int64}}, Base.Slice{Base.OneTo{Int64}}})
   @ Base ./abstractarray.jl:703
 [2] checkbounds
   @ ./abstractarray.jl:668 [inlined]
 [3] _getindex
   @ ./multidimensional.jl:874 [inlined]
 [4] getindex(::Vector{Float64}, ::Int64, ::Function, ::Function)
   @ Base ./abstractarray.jl:1241
 [5] top-level scope
   @ ~/Desktop/Articles_Code/Codes/Julia/projects/Electric_field.jl:15

```

Can someone help?

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**Author:** ![DNF](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dnf/32/10191_2.png) [@DNF](https://discourse.julialang.org/u/DNF)\
**Post date:** [April 23, 2023, 7:39am UTC](https://discourse.julialang.org/t/work-around-for-meshgrid-of-python-into-julia/97807/2 "2023-04-23T07:39:18Z")

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The error message tells you how the error occurs:

> [@aburousan](#):
>
> `BoundsError: attempt to access 100-element Vector{Float64} at index [0, 1:1, 1:1]`

> [@aburousan](#):
>
> ```julia
> grids = 1 .- (zv /100)
> contour(grids[0,:,:])
> 
> ```

You have created a grid, `grids`, but here you replace that grid with `grids = 1 .- (zv /100)`, so the 3D grid is now gone. The actual error then is triggered on the next line, since Julia `Array`s have one-based indexing, but you are giving it 0, which is a `BoundsError`.

I’m not sure exactly what you would like to do, but if you are looking to plot a slice of the original grid, maybe first remove the redefinition of `grids`, and then try

```julia
contour(grids[1,:,:]) 

```

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<div class="post-metadata">

**Author:** ![DNF](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dnf/32/10191_2.png) [@DNF](https://discourse.julialang.org/u/DNF)\
**Post date:** [April 23, 2023, 7:44am UTC](https://discourse.julialang.org/t/work-around-for-meshgrid-of-python-into-julia/97807/3 "2023-04-23T07:44:33Z")

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> [@aburousan](#):
>
> `xv = yv = zv = collect(1:N)`

BTW, there are two issues with this line. Firstly, it allocates a `Vector`, probably needlessly. You can in most cases just use `1:N` instead of `collect(1:N)`. It’s faster and better. Secondly, you are making `xv`, `yv`, and `zv` all point to the exact same vector, which means that if you modify one of them, all three are affected.

My general advice is ‘never use `collect`’. Only use it if your code cannot work without it.

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**Author:** ![aburousan](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/aburousan/32/28525_2.png) [@aburousan](https://discourse.julialang.org/u/aburousan)\
**Post date:** [April 23, 2023, 7:46am UTC](https://discourse.julialang.org/t/work-around-for-meshgrid-of-python-into-julia/97807/4 "2023-04-23T07:46:21Z")

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Seriously… I am a fool… Yes… That 0 and i never noticed 😑😥

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**Author:** ![DNF](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dnf/32/10191_2.png) [@DNF](https://discourse.julialang.org/u/DNF)\
**Post date:** [April 23, 2023, 8:11am UTC](https://discourse.julialang.org/t/work-around-for-meshgrid-of-python-into-julia/97807/5 "2023-04-23T08:11:35Z")

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One more thing. I’m not exactly sure why you are moving code from numpy to Julia, but if it is for performance reasons, you should be aware that writing Julia in ‘numpy-style’ is not likely to speed it up. In fact, the Julia version will probably be slower, since Julia slices create copies.

If you want fast code, you should read the [performance tips](https://docs.julialang.org/en/v1/manual/performance-tips/) in the manual.

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<div class="post-metadata">

**Author:** ![aburousan](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/aburousan/32/28525_2.png) [@aburousan](https://discourse.julialang.org/u/aburousan)\
**Post date:** [April 23, 2023, 8:38am UTC](https://discourse.julialang.org/t/work-around-for-meshgrid-of-python-into-julia/97807/6 "2023-04-23T08:38:31Z")

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But still it’s not giving me same plot…

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<div class="post-metadata">

**Author:** ![DNF](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dnf/32/10191_2.png) [@DNF](https://discourse.julialang.org/u/DNF)\
**Post date:** [April 23, 2023, 11:13am UTC](https://discourse.julialang.org/t/work-around-for-meshgrid-of-python-into-julia/97807/7 "2023-04-23T11:13:35Z")

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What is your updated code? Please include the library imports as well. Which plot library are you using?