# Latest

**URL:** https://discourse.julialang.org/latest.md?page=1860

[Latest](https://discourse.julialang.org/latest.md) · [Categories](https://discourse.julialang.org/categories.md) · [Tags](https://discourse.julialang.org/tags.md)

**Page:** 1861

---

## [What is the type of #undef](https://discourse.julialang.org/t/what-is-the-type-of-undef/32411)

<div class="topic-metadata">

**Author:** [@Qiyamah](https://discourse.julialang.org/u/Qiyamah)\
**Replies:** 9\
**Last updated:** [December 18, 2019, 7:14am UTC](https://discourse.julialang.org/t/what-is-the-type-of-undef/32411 "2019-12-18T07:14:43Z")

</div>

struct MMX x MMX() = new() end t = MMX() \> MMX(#undef) typeof(t.x) Basically I am asking what is the type of field x in this case?

---

## [Writing effective parallel code](https://discourse.julialang.org/t/writing-effective-parallel-code/32407)

<div class="topic-metadata">

**Author:** [@cgeoga](https://discourse.julialang.org/u/cgeoga)\
**Replies:** 8\
**Last updated:** [December 18, 2019, 4:38am UTC](https://discourse.julialang.org/t/writing-effective-parallel-code/32407 "2019-12-18T04:38:41Z")

</div>

I’m trying to think more seriously about writing Julia code that is either thread or worker parallel to make better use of high thread machines or individual cluster nodes with many CPUs. While I recognize that in genera…

---

## [How does SVector manage memory?](https://discourse.julialang.org/t/how-does-svector-manage-memory/32376)

<div class="topic-metadata">

**Author:** [@tomtom](https://discourse.julialang.org/u/tomtom)\
**Replies:** 7\
**Last updated:** [December 18, 2019, 2:26am UTC](https://discourse.julialang.org/t/how-does-svector-manage-memory/32376 "2019-12-18T02:26:47Z")

</div>

julia\> using StaticArrays julia\> using BenchmarkTools julia\> x = \[1, 2, 3\] julia\> y = SVector{3, Int64}(x) julia\> @btime exp.($x); 62.574 ns (1 allocation: 112 bytes) julia\> @btime exp.($y); 0.022 ns (0 allocation…

---

## [Is it possible to format axis labels as a currency in Plots.jl](https://discourse.julialang.org/t/is-it-possible-to-format-axis-labels-as-a-currency-in-plots-jl/32408)

<div class="topic-metadata">

**Author:** [@atteson](https://discourse.julialang.org/u/atteson)\
**Replies:** 1\
**Last updated:** [December 17, 2019, 9:42pm UTC](https://discourse.julialang.org/t/is-it-possible-to-format-axis-labels-as-a-currency-in-plots-jl/32408 "2019-12-17T21:42:26Z")

</div>

I saw an online discussion of formatters from 2016 but didn’t see anything in the package.

---

## [Pkg.add("Gtk") / Unsatisfiable requirement](https://discourse.julialang.org/t/pkg-add-gtk-unsatisfiable-requirement/32394)

<div class="topic-metadata">

**Author:** [@Qiyamah](https://discourse.julialang.org/u/Qiyamah)\
**Replies:** 3\
**Last updated:** [December 17, 2019, 9:18pm UTC](https://discourse.julialang.org/t/pkg-add-gtk-unsatisfiable-requirement/32394 "2019-12-17T21:18:42Z")

</div>

import Pkg Pkg.add(“Gtk”) results in… ERROR: Unsatisfiable requirements detected for package Homebrew \[d9be37ee\]: Homebrew \[d9be37ee\] log: ├─possible versions are: \[0.6.4, 0.6.6, 0.7.0-0.7.1\] or uninstalled ├─restr…

---

## [Current state of JuliaLang/METADATA.jl](https://discourse.julialang.org/t/current-state-of-julialang-metadata-jl/32391)

<div class="topic-metadata">

**Author:** [@mattBrzezinski](https://discourse.julialang.org/u/mattBrzezinski)\
**Replies:** 2\
**Last updated:** [December 17, 2019, 9:10pm UTC](https://discourse.julialang.org/t/current-state-of-julialang-metadata-jl/32391 "2019-12-17T21:10:03Z")

</div>

I wanted to start a discussion on the current state of METADATA.jl, I’ve recently been making changes to AWSSQS.jl and have been receiving new issues from attobot that the package URL does not match what is stored in MET…

---

## [When are round brackets required for VegaLite?](https://discourse.julialang.org/t/when-are-round-brackets-required-for-vegalite/32401)

<div class="topic-metadata">

**Author:** [@affans](https://discourse.julialang.org/u/affans)\
**Replies:** 3\
**Last updated:** [December 17, 2019, 8:07pm UTC](https://discourse.julialang.org/t/when-are-round-brackets-required-for-vegalite/32401 "2019-12-17T20:07:23Z")

</div>

In this example, why are the brackets ( and ) needed to surround the extra @vlplot commands? using VegaDatasets dataset("weather.csv") |\> @vlplot(repeat={column=\[:temp\_max,:precipitation,:wind\]}) + ( @vlplot() + …

---

## [Plotlyjs.jl - generate composite figure with violin and scatter](https://discourse.julialang.org/t/plotlyjs-jl-generate-composite-figure-with-violin-and-scatter/32402)

<div class="topic-metadata">

**Author:** [@josephmarturano](https://discourse.julialang.org/u/josephmarturano)\
**Replies:** 0\
**Last updated:** [December 17, 2019, 7:41pm UTC](https://discourse.julialang.org/t/plotlyjs-jl-generate-composite-figure-with-violin-and-scatter/32402 "2019-12-17T19:41:22Z")

</div>

I would like to use PlotlyJS.jl to generate a composite figure with a violin and scatterplot, where the scatterplot is overlayed on top of the violin and is actually the mean ± 95% confidence interval of the mean. My cur…

---

## [VegaLite throws error on faceting plots](https://discourse.julialang.org/t/vegalite-throws-error-on-faceting-plots/32396)

<div class="topic-metadata">

**Author:** [@affans](https://discourse.julialang.org/u/affans)\
**Replies:** 2\
**Last updated:** [December 17, 2019, 7:30pm UTC](https://discourse.julialang.org/t/vegalite-throws-error-on-faceting-plots/32396 "2019-12-17T19:30:02Z")

</div>

The following code plots data on a single plot. The data is melted data with column names Symbol\[:variable, :value, :time\]. I particularly want lines and points for each dataset… I know I can used filled=true but I am a…

---

## [Tips/guidance for identifying the source of a deadlock when multithreading?](https://discourse.julialang.org/t/tips-guidance-for-identifying-the-source-of-a-deadlock-when-multithreading/32358)

<div class="topic-metadata">

**Author:** [@vlandau](https://discourse.julialang.org/u/vlandau)\
**Replies:** 0\
**Last updated:** [December 16, 2019, 10:34pm UTC](https://discourse.julialang.org/t/tips-guidance-for-identifying-the-source-of-a-deadlock-when-multithreading/32358 "2019-12-16T22:34:27Z")

</div>

I suspect that my Julia package, Omniscape.jl, is running into a deadlock when testing on Windows in Julia 1.3 (everything passes in 1.2) in Travis and Appveyor. Basically, it just hangs a few dozen iterations into a @th…

---

## [How to recompile a package I am developing](https://discourse.julialang.org/t/how-to-recompile-a-package-i-am-developing/32385)

<div class="topic-metadata">

**Author:** [@gmouts](https://discourse.julialang.org/u/gmouts)\
**Replies:** 2\
**Last updated:** [December 17, 2019, 2:54pm UTC](https://discourse.julialang.org/t/how-to-recompile-a-package-i-am-developing/32385 "2019-12-17T14:54:49Z")

</div>

I guess it is an elementary question but I couldn’t figure it out. I am developing a package. How can I tell Julia to recompile it after I made some changes to the code?

---

## [MethodError: no method matching length(::CSV.Row{false})](https://discourse.julialang.org/t/methoderror-no-method-matching-length-csv-row-false/32386)

<div class="topic-metadata">

**Author:** [@bsnyh](https://discourse.julialang.org/u/bsnyh)\
**Replies:** 0\
**Last updated:** [December 17, 2019, 2:57pm UTC](https://discourse.julialang.org/t/methoderror-no-method-matching-length-csv-row-false/32386 "2019-12-17T14:57:56Z")

</div>

using CSV using DataFrames fln = "myfln.csv" for (i,row) in enumerate(CSV.File(fln)) if df.Resource\[i\] == 1 push!(df1,row) elseif df.Resource\[i\] == 2 push!(df2,row) elseif df.Resource\[i\] == …

---

## [ModelingToolkit: variables in an expression and expression simplification](https://discourse.julialang.org/t/modelingtoolkit-variables-in-an-expression-and-expression-simplification/31894)

<div class="topic-metadata">

**Author:** [@cvanaret](https://discourse.julialang.org/u/cvanaret)\
**Replies:** 6\
**Last updated:** [December 17, 2019, 12:26pm UTC](https://discourse.julialang.org/t/modelingtoolkit-variables-in-an-expression-and-expression-simplification/31894 "2019-12-17T12:26:43Z")

</div>

Hi, I have two questions about the ModelingToolkit package: is there a function that determines the list of variables that occur in an expression? Example: x^2 + y - exp(y) contains x and y is there a function th…

---

## [Perhaps a new way of composing functions](https://discourse.julialang.org/t/perhaps-a-new-way-of-composing-functions/32366)

<div class="topic-metadata">

**Author:** [@StevenSiew](https://discourse.julialang.org/u/StevenSiew)\
**Replies:** 2\
**Last updated:** [December 17, 2019, 10:20am UTC](https://discourse.julialang.org/t/perhaps-a-new-way-of-composing-functions/32366 "2019-12-17T10:20:16Z")

</div>

julia\> msg = "Hello!" "Hello!" julia\> print("Normal: "); println(uppercase(msg)) Normal: HELLO! julia\> print("Piping: "); msg |\> uppercase |\> println Piping: HELLO! julia\> print("Compose: "); (println ∘ uppercase)(msg…

---

## [GraphViz.jl](https://discourse.julialang.org/t/graphviz-jl/32374)

<div class="topic-metadata">

**Author:** [@Qiyamah](https://discourse.julialang.org/u/Qiyamah)\
**Replies:** 1\
**Last updated:** [December 17, 2019, 8:22am UTC](https://discourse.julialang.org/t/graphviz-jl/32374 "2019-12-17T08:22:34Z")

</div>

I would like to use GraphViz.jl, however Pkg.add(“GraphViz”) results in ERROR: The following package names could not be resolved: \* GraphViz (not found in project, manifest or registry) Please specify by known \`name=u…

---

## [Error in Android studio](https://discourse.julialang.org/t/error-in-android-studio/32372)

<div class="topic-metadata">

**Author:** [@William\_willson](https://discourse.julialang.org/u/William_willson)\
**Replies:** 4\
**Last updated:** [December 17, 2019, 7:41am UTC](https://discourse.julialang.org/t/error-in-android-studio/32372 "2019-12-17T07:41:37Z")

</div>

There was something went to wrong Julia does not find its executable to run Julia code to build application

---

## [PackageCompiler error on Windows - Task cannot be serialized](https://discourse.julialang.org/t/packagecompiler-error-on-windows-task-cannot-be-serialized/32031)

<div class="topic-metadata">

**Author:** [@Iulian.Cioarca](https://discourse.julialang.org/u/Iulian.Cioarca)\
**Replies:** 2\
**Last updated:** [December 17, 2019, 6:42am UTC](https://discourse.julialang.org/t/packagecompiler-error-on-windows-task-cannot-be-serialized/32031 "2019-12-17T06:42:39Z")

</div>

I know there were older posts about this, but I could not find a solution. Has anyone managed to compile Plots to a system image on windows? I tried on a fresh install of Julia 1.3 (.julia folder deleted and added only t…

---

## [Open Positions at Beacon Biosignals](https://discourse.julialang.org/t/open-positions-at-beacon-biosignals/31859)

<div class="topic-metadata">

**Author:** [@jrevels](https://discourse.julialang.org/u/jrevels)\
**Replies:** 6\
**Last updated:** [December 17, 2019, 3:50am UTC](https://discourse.julialang.org/t/open-positions-at-beacon-biosignals/31859 "2019-12-17T03:50:16Z")

</div>

Beacon Biosignals is seeking talented DevOps/Julia folks to help us take the task of analyzing hundreds of terabytes of EEG data from “ouch that hurts, my poor RAM, oof” to “painless, my containers are one big happy fami…

---

## [Collections of quadratic expressions causes @expression to throw error](https://discourse.julialang.org/t/collections-of-quadratic-expressions-causes-expression-to-throw-error/32359)

<div class="topic-metadata">

**Author:** [@Stivanification](https://discourse.julialang.org/u/Stivanification)\
**Replies:** 2\
**Last updated:** [December 16, 2019, 11:51pm UTC](https://discourse.julialang.org/t/collections-of-quadratic-expressions-causes-expression-to-throw-error/32359 "2019-12-16T23:51:27Z")

</div>

Hi, As the title says, I’m getting an error trying to create an array of quadratic expressions in JuMP. I’m using julia v1.1.0 and JuMP v0.20.1. Minimal example: using JuMP model = Model() @variables(model, begin …

---

## [Multiplying by a variable in a constraint causing type instability in @code\_warntype](https://discourse.julialang.org/t/multiplying-by-a-variable-in-a-constraint-causing-type-instability-in-code-warntype/32239)

<div class="topic-metadata">

**Author:** [@stop\_movn](https://discourse.julialang.org/u/stop_movn)\
**Replies:** 9\
**Last updated:** [December 16, 2019, 10:48pm UTC](https://discourse.julialang.org/t/multiplying-by-a-variable-in-a-constraint-causing-type-instability-in-code-warntype/32239 "2019-12-16T22:48:16Z")

</div>

I am trying to figure out how to avoid type instability in my model that uses some constraints and objectives that include a variable. I can’t seem to avoid a “::Union{Val{false}, GenericAffExpr{Float64,VariableRef}}” e…

---

## [What means 'at' and 'rt' in \`@cfunction\`?](https://discourse.julialang.org/t/what-means-at-and-rt-in-cfunction/32345)

<div class="topic-metadata">

**Author:** [@swissr](https://discourse.julialang.org/u/swissr)\
**Replies:** 2\
**Last updated:** [December 16, 2019, 9:56pm UTC](https://discourse.julialang.org/t/what-means-at-and-rt-in-cfunction/32345 "2019-12-16T21:56:29Z")

</div>

A tiny detail, but I wonder, for what the “at” and “rt” argument names stand in the cfunction macro? From the help (@cfunction(callable, ReturnType, (ArgumentTypes...,)) -\> Ptr{Cvoid}…) I would have thought “argument ty…

---

## [Relative/absolute tolerance per element](https://discourse.julialang.org/t/relative-absolute-tolerance-per-element/32356)

<div class="topic-metadata">

**Author:** [@fishy](https://discourse.julialang.org/u/fishy)\
**Replies:** 0\
**Last updated:** [December 16, 2019, 9:32pm UTC](https://discourse.julialang.org/t/relative-absolute-tolerance-per-element/32356 "2019-12-16T21:32:12Z")

</div>

I am using differentialequations.jl as the core of a 6DOF simulator for my company. We need to evaluate the behaviour of some very different sized vehicles and thus can run the solver with different tolerances. The state…

---

## [Unification or pattern matching for matching \`UnionAll\` types against each other](https://discourse.julialang.org/t/unification-or-pattern-matching-for-matching-unionall-types-against-each-other/32217)

<div class="topic-metadata">

**Author:** [@goretkin](https://discourse.julialang.org/u/goretkin)\
**Replies:** 8\
**Last updated:** [December 16, 2019, 8:23pm UTC](https://discourse.julialang.org/t/unification-or-pattern-matching-for-matching-unionall-types-against-each-other/32217 "2019-12-16T20:23:43Z")

</div>

There’s some type-system functionality which I believe exists in Julia, that I’d like to try to access. I don’t know of a better way to explain it than jumping straight to a code example. connection(x, y) = false connec…

---

## [Slides about a talk introducing Julia to Python programmers](https://discourse.julialang.org/t/slides-about-a-talk-introducing-julia-to-python-programmers/32352)

<div class="topic-metadata">

**Author:** [@dmolina](https://discourse.julialang.org/u/dmolina)\
**Replies:** 0\
**Last updated:** [December 16, 2019, 8:03pm UTC](https://discourse.julialang.org/t/slides-about-a-talk-introducing-julia-to-python-programmers/32352 "2019-12-16T20:03:48Z")

</div>

Several weeks ago I did a talk about Julia in my Faculty, and it was great. The majority of assistants were students of Computer Science and Data Science Master, so in the talk Julia is mainly compared against Python. I …

---

## [How do I skip an iteration of enumerator](https://discourse.julialang.org/t/how-do-i-skip-an-iteration-of-enumerator/32341)

<div class="topic-metadata">

**Author:** [@feanor12](https://discourse.julialang.org/u/feanor12)\
**Replies:** 4\
**Last updated:** [December 16, 2019, 5:58pm UTC](https://discourse.julialang.org/t/how-do-i-skip-an-iteration-of-enumerator/32341 "2019-12-16T17:58:15Z")

</div>

Hi, I have the problem that I have an array which is changing during a loop and I have to skip certain elements. What is the best way to do this? a = \[1,2,3\] itr = Iterators.Stateful(a) for (i,el) in enumerate(itr) …

---

## [Subtyping with union as type parameter](https://discourse.julialang.org/t/subtyping-with-union-as-type-parameter/32326)

<div class="topic-metadata">

**Author:** [@rapus95](https://discourse.julialang.org/u/rapus95)\
**Replies:** 3\
**Last updated:** [December 16, 2019, 5:48pm UTC](https://discourse.julialang.org/t/subtyping-with-union-as-type-parameter/32326 "2019-12-16T17:48:31Z")

</div>

abstract type AbstractGrid{T, F, V} \<: AbstractArray{Union{T,Missing},2} end Why the Union{T,Missing} impedes the compilation here? I always get a UndefRefError: access to undefined reference. EDIT: Seems to be relate…

---

## [Could performance of globals be improved by a 265 like approach?](https://discourse.julialang.org/t/could-performance-of-globals-be-improved-by-a-265-like-approach/32292)

<div class="topic-metadata">

**Author:** [@Oscar\_Smith](https://discourse.julialang.org/u/Oscar_Smith)\
**Replies:** 9\
**Last updated:** [December 16, 2019, 4:34pm UTC](https://discourse.julialang.org/t/could-performance-of-globals-be-improved-by-a-265-like-approach/32292 "2019-12-16T16:34:52Z")

</div>

As I understand it, the fundamental problem with performance of variables in the global scope is that dynamic checks and then dispatch have to be done, since the types of globals can change after definition. What would h…

---

## [Make an animation fade](https://discourse.julialang.org/t/make-an-animation-fade/32192)

<div class="topic-metadata">

**Author:** [@Torkel](https://discourse.julialang.org/u/Torkel)\
**Replies:** 3\
**Last updated:** [December 16, 2019, 4:30pm UTC](https://discourse.julialang.org/t/make-an-animation-fade/32192 "2019-12-16T16:30:22Z")

</div>

I have managed to create an animation object, either through: anim\_ode = animate(ode\_sol\_1,kwargs...) #using a solution of a differential equation. anim\_macro = @animate for t\_end in 0.:45 plot(0.:0.1:t\_end,t-\>(sin(…

---

## [Displaying two animations simultaneously](https://discourse.julialang.org/t/displaying-two-animations-simultaneously/32191)

<div class="topic-metadata">

**Author:** [@Torkel](https://discourse.julialang.org/u/Torkel)\
**Replies:** 1\
**Last updated:** [December 16, 2019, 4:27pm UTC](https://discourse.julialang.org/t/displaying-two-animations-simultaneously/32191 "2019-12-16T16:27:53Z")

</div>

I have managed to create two animation objects, is there an easy way to display these simultaneously? either with animation object created through differential equations solutions anim1 = animate(ode\_sol\_1,kwargs...) a…

---

## [Having trouble installing the PortAudio package](https://discourse.julialang.org/t/having-trouble-installing-the-portaudio-package/31969)

<div class="topic-metadata">

**Author:** [@CoffeeTurtle1](https://discourse.julialang.org/u/CoffeeTurtle1)\
**Replies:** 30\
**Last updated:** [December 16, 2019, 3:54pm UTC](https://discourse.julialang.org/t/having-trouble-installing-the-portaudio-package/31969 "2019-12-16T15:54:24Z")

</div>

Hello, I cannot add the PortAudio package. When I run add https://github.com/JuliaAudio/PortAudio.jl I get this error: ERROR: failed to clone from https://github.com/JuliaAudio/PortAudio.jl, error: GitError(Code:ERROR…

[Previous page](https://discourse.julialang.org/latest.md?page=1859)

[Next page](https://discourse.julialang.org/latest.md?page=1861)