# Latest

**URL:** https://discourse.julialang.org/latest.md?page=1640

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

**Page:** 1641

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## [Question about Image output](https://discourse.julialang.org/t/question-about-image-output/46055)

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**Author:** [@abcde](https://discourse.julialang.org/u/abcde)\
**Replies:** 4\
**Last updated:** [September 5, 2020, 3:54am UTC](https://discourse.julialang.org/t/question-about-image-output/46055 "2020-09-05T03:54:30Z")

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May I ask if Julia can realize dynamic 3D map? For example, you can interact with the mouse or rotate advanced images by yourself. thank you！！

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## [Stipple.jl Issues on Heroku](https://discourse.julialang.org/t/stipple-jl-issues-on-heroku/46086)

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**Author:** [@nucklass](https://discourse.julialang.org/u/nucklass)\
**Replies:** 0\
**Last updated:** [September 5, 2020, 3:10am UTC](https://discourse.julialang.org/t/stipple-jl-issues-on-heroku/46086 "2020-09-05T03:10:59Z")

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Hi all, I’ve been trying out stipple the last few days as an alternative to RShiny and Tableau. I’ve been able to get a nice little dashboard and I wanted to post it online to share with a few other students. By followi…

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## [A simple macro to transform \`newcol = fn(:col)\` to \`:col =\> fn =\> :newcol\`; friendly with DataFrames.jl](https://discourse.julialang.org/t/a-simple-macro-to-transform-newcol-fn-col-to-col-fn-newcol-friendly-with-dataframes-jl/45893)

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**Author:** [@xiaodai](https://discourse.julialang.org/u/xiaodai)\
**Replies:** 1\
**Last updated:** [September 5, 2020, 2:52am UTC](https://discourse.julialang.org/t/a-simple-macro-to-transform-newcol-fn-col-to-col-fn-newcol-friendly-with-dataframes-jl/45893 "2020-09-05T02:52:30Z")

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In DataFrames.jl there are a number of places where you have use this syntax :col =\> fn =\> :newcol to compute new columns. This makes sense once you get used to it, but sometimes you want a traditional syntax of newcol =…

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## [Apache Arrow 1.0 release](https://discourse.julialang.org/t/apache-arrow-1-0-release/43786)

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**Author:** [@dmbates](https://discourse.julialang.org/u/dmbates)\
**Replies:** 7\
**Last updated:** [September 5, 2020, 1:28am UTC](https://discourse.julialang.org/t/apache-arrow-1-0-release/43786 "2020-09-05T01:28:45Z")

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Version 1.0.0 of the Apache Arrow specification and implementations in several languages has been released Apache Arrow 1.0.0 Release | Apache Arrow As part of this release the Feather file specification (a file format …

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## [Regression Random Forests: Mean coeff of determination in cross-validation surprisingly too good for pure noise inputs](https://discourse.julialang.org/t/regression-random-forests-mean-coeff-of-determination-in-cross-validation-surprisingly-too-good-for-pure-noise-inputs/46073)

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**Author:** [@rio](https://discourse.julialang.org/u/rio)\
**Replies:** 1\
**Last updated:** [September 4, 2020, 11:26pm UTC](https://discourse.julialang.org/t/regression-random-forests-mean-coeff-of-determination-in-cross-validation-surprisingly-too-good-for-pure-noise-inputs/46073 "2020-09-04T23:26:46Z")

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I fitted a regression RF model on random (low dimensional) noise data and got surprising good estimates of the Mean Coeff of Determination using Cross-Validation. Here is my code, based on the example in https://github.…

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## [Recording entry and exit time of state space sets with DifferentialEquations.jl](https://discourse.julialang.org/t/recording-entry-and-exit-time-of-state-space-sets-with-differentialequations-jl/46029)

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**Author:** [@Datseris](https://discourse.julialang.org/u/Datseris)\
**Replies:** 14\
**Last updated:** [September 4, 2020, 11:05pm UTC](https://discourse.julialang.org/t/recording-entry-and-exit-time-of-state-space-sets-with-differentialequations-jl/46029 "2020-09-04T23:05:55Z")

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I am trying to estimate entry and exit times in sets of the state space, as functionality for DynamicalSystems.jl. I have a working implementation for discrete systems but for continuous it turns out it is much harder. O…

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## [Generate new array using conditional selections from existing arrays](https://discourse.julialang.org/t/generate-new-array-using-conditional-selections-from-existing-arrays/46081)

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**Author:** [@yold6](https://discourse.julialang.org/u/yold6)\
**Replies:** 2\
**Last updated:** [September 4, 2020, 10:43pm UTC](https://discourse.julialang.org/t/generate-new-array-using-conditional-selections-from-existing-arrays/46081 "2020-09-04T22:43:41Z")

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Hello, I am attempting to generate an new array C by using conditional selections from two existing DataFrames (A and B). The first pre-existing DataFrame (A) is 18 x 18 and contains Float64 values that I would like to…

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## [How to write device code?](https://discourse.julialang.org/t/how-to-write-device-code/11527)

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**Author:** [@floswald](https://discourse.julialang.org/u/floswald)\
**Replies:** 4\
**Last updated:** [September 4, 2020, 10:32pm UTC](https://discourse.julialang.org/t/how-to-write-device-code/11527 "2020-09-04T22:32:48Z")

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hi there newcomer question here. suppose i am looking at some cuda code that has a function like \_\_device\_\_ int binaryVal(const REAL x, const int n, const REAL\* X) { } where I read the \_\_device\_\_ thing as saying that …

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## [Using LightXML I error out when using "free(xdoc)" in Atom, but not in terminal?](https://discourse.julialang.org/t/using-lightxml-i-error-out-when-using-free-xdoc-in-atom-but-not-in-terminal/46075)

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**Author:** [@Ahmed\_Salih](https://discourse.julialang.org/u/Ahmed_Salih)\
**Replies:** 0\
**Last updated:** [September 4, 2020, 8:00pm UTC](https://discourse.julialang.org/t/using-lightxml-i-error-out-when-using-free-xdoc-in-atom-but-not-in-terminal/46075 "2020-09-04T20:00:36Z")

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Hello! I am trying to play around with making xml files. I have made this simple XML: using LightXML # create an empty XML document xdoc = XMLDocument() # create & attach a root node xroot = create\_root(xdoc, "case")…

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## [Pipe operator quiz! Can you guess the result?](https://discourse.julialang.org/t/pipe-operator-quiz-can-you-guess-the-result/46054)

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**Author:** [@sijo](https://discourse.julialang.org/u/sijo)\
**Replies:** 6\
**Last updated:** [September 4, 2020, 5:20pm UTC](https://discourse.julialang.org/t/pipe-operator-quiz-can-you-guess-the-result/46054 "2020-09-04T17:20:37Z")

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Question 1 A=\[1,2,3\]; B=\[1,1,1\]; A.\>B |\> sum Question 2 1:2 .|\> x-\>x^2 |\> sum |\> inv Question 3 (warning: spoilers) The behaviors above seem just… evil! :wink:. Can we fix this? Changing the operator precedence is …

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## [Tennis Lineup Optimizer](https://discourse.julialang.org/t/tennis-lineup-optimizer/46036)

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**Author:** [@Cameron\_Taylor](https://discourse.julialang.org/u/Cameron_Taylor)\
**Replies:** 2\
**Last updated:** [September 4, 2020, 4:03pm UTC](https://discourse.julialang.org/t/tennis-lineup-optimizer/46036 "2020-09-04T16:03:31Z")

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Hi all, I’m putting together a little tennis lineup optimizer program to play some daily fantasy contests during the US Open here. I’m trying to write a constraint that picks a set of players on the condition that a pl…

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## [Changing size of ODE system: resize! works but deleteat! doesn't](https://discourse.julialang.org/t/changing-size-of-ode-system-resize-works-but-deleteat-doesnt/45900)

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**Author:** [@levasco](https://discourse.julialang.org/u/levasco)\
**Replies:** 5\
**Last updated:** [September 4, 2020, 3:54pm UTC](https://discourse.julialang.org/t/changing-size-of-ode-system-resize-works-but-deleteat-doesnt/45900 "2020-09-04T15:54:51Z")

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I am playing around with the capacity of changing the size of an ODE system by tweaking the example presented here. For some reason, shrinking the model by resize!()ing the integrator works as expected, but the (equivale…

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## [\[ANN\] Configs.jl: Opinionated tool for managing deployment configurations](https://discourse.julialang.org/t/ann-configs-jl-opinionated-tool-for-managing-deployment-configurations/45847)

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**Author:** [@citkane](https://discourse.julialang.org/u/citkane)\
**Replies:** 12\
**Last updated:** [September 4, 2020, 3:29pm UTC](https://discourse.julialang.org/t/ann-configs-jl-opinionated-tool-for-managing-deployment-configurations/45847 "2020-09-04T15:29:34Z")

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I am new to Julia, so firstly a “Hello” to everybody in the community. Coming from a Node.js background, I miss some generic tools that I have become accustomed to, specifically managing deployment configurations with t…

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## [Remove spaces and units in Dataframe header?](https://discourse.julialang.org/t/remove-spaces-and-units-in-dataframe-header/46061)

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**Author:** [@Ahmed\_Salih](https://discourse.julialang.org/u/Ahmed_Salih)\
**Replies:** 6\
**Last updated:** [September 4, 2020, 2:11pm UTC](https://discourse.julialang.org/t/remove-spaces-and-units-in-dataframe-header/46061 "2020-09-04T14:11:45Z")

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Hello! I am using DataFrames on a CSV file with space and unit declarations next to the variable, for an example: time \[s\] So when I import it, it looks like: How would I go about removing " \[s\]", so it would becom…

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## [Continue a loop in Julia when the time out](https://discourse.julialang.org/t/continue-a-loop-in-julia-when-the-time-out/46002)

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**Author:** [@yangqifan](https://discourse.julialang.org/u/yangqifan)\
**Replies:** 6\
**Last updated:** [September 4, 2020, 1:58pm UTC](https://discourse.julialang.org/t/continue-a-loop-in-julia-when-the-time-out/46002 "2020-09-04T13:58:25Z")

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When I use the DifferentialEquations.jl to solve a ODEs, some parameters set is time-consuming. I have write a loop to solve the ODEs at diverse parameters. I want to early terminate the time-consuming parameters set, fo…

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## [Regular expression How do I find a line that contains this rule but also something else?](https://discourse.julialang.org/t/regular-expression-how-do-i-find-a-line-that-contains-this-rule-but-also-something-else/46010)

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**Author:** [@programista](https://discourse.julialang.org/u/programista)\
**Replies:** 10\
**Last updated:** [September 4, 2020, 1:06pm UTC](https://discourse.julialang.org/t/regular-expression-how-do-i-find-a-line-that-contains-this-rule-but-also-something-else/46010 "2020-09-04T13:06:38Z")

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How do I find a line that contains this rule but also something else? rx=r"^\[0-9\]{2}-\[0-9\]{3}$" occursin.( rx ,string.(dane\[:,6\])) Thx, Paul

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## [Build from a master or development branch](https://discourse.julialang.org/t/build-from-a-master-or-development-branch/46056)

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**Author:** [@jheinen](https://discourse.julialang.org/u/jheinen)\
**Replies:** 1\
**Last updated:** [September 4, 2020, 12:51pm UTC](https://discourse.julialang.org/t/build-from-a-master-or-development-branch/46056 "2020-09-04T12:51:33Z")

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How can I force BinaryBuilder to make a local build for a development branch? using BinaryBuilder name = "my\_package" version = v"?.?.?" \<= e.g., my\_package#development

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## [Array{Float64,2} -\> Array{Float64,1}](https://discourse.julialang.org/t/array-float64-2-array-float64-1/45979)

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**Author:** [@Jhall7529](https://discourse.julialang.org/u/Jhall7529)\
**Replies:** 5\
**Last updated:** [September 4, 2020, 12:48pm UTC](https://discourse.julialang.org/t/array-float64-2-array-float64-1/45979 "2020-09-04T12:48:41Z")

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When indexing an Array{Float64,2} julia\> A = ones(1,5) 1×5 Array{Float64,2}: 1.0 1.0 1.0 1.0 1.0 julia\> A\[1,2:5\] 4-element Array{Float64,1}: 1.0 1.0 1.0 1.0 Why am I being given an Array{Float64,1}? I’m ex…

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## ["Python is undoubtedly faster in helping programmers express their concept in fewer lines of code"](https://discourse.julialang.org/t/python-is-undoubtedly-faster-in-helping-programmers-express-their-concept-in-fewer-lines-of-code/45872)

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**Author:** [@DaymondLing](https://discourse.julialang.org/u/DaymondLing)\
**Replies:** 27\
**Last updated:** [September 4, 2020, 12:48pm UTC](https://discourse.julialang.org/t/python-is-undoubtedly-faster-in-helping-programmers-express-their-concept-in-fewer-lines-of-code/45872 "2020-09-04T12:48:30Z")

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Julia vs Python: Which is best for Data Science? | TechGig says “Python is undoubtedly faster in helping programmers express their concept in fewer lines of code”. Really? I find Julia can express mathematical ideas ve…

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## [@show\_code macro](https://discourse.julialang.org/t/show-code-macro/46050)

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**Author:** [@Impressium](https://discourse.julialang.org/u/Impressium)\
**Replies:** 2\
**Last updated:** [September 4, 2020, 11:50am UTC](https://discourse.julialang.org/t/show-code-macro/46050 "2020-09-04T11:50:45Z")

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Hey :slight\_smile: Is there a @show\_code yet? e.g.: julia\> @show\_code sqrt(1+1) sqrt(1+1) in Main at REPL\[10\]:1 In file.jl 1: 2:@show\_code sqrt(1+1) 3: after running returns: sqrt(1+1) in file.jl:2 So I can do: …

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## [Fetch value stored in a File or FileTree node on Windows 10](https://discourse.julialang.org/t/fetch-value-stored-in-a-file-or-filetree-node-on-windows-10/46045)

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**Author:** [@evad](https://discourse.julialang.org/u/evad)\
**Replies:** 0\
**Last updated:** [September 4, 2020, 8:26am UTC](https://discourse.julialang.org/t/fetch-value-stored-in-a-file-or-filetree-node-on-windows-10/46045 "2020-09-04T08:26:29Z")

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I have stored a dataframe in the following file node. But can’t retrieve it using the get function. What did I do wrong? thanks

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## [3D Quiver Plot and animation](https://discourse.julialang.org/t/3d-quiver-plot-and-animation/44645)

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**Author:** [@sriharitn](https://discourse.julialang.org/u/sriharitn)\
**Replies:** 5\
**Last updated:** [September 4, 2020, 8:47am UTC](https://discourse.julialang.org/t/3d-quiver-plot-and-animation/44645 "2020-09-04T08:47:17Z")

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I’m trying to plot 3D Quiver plot with Julia Plots package, it appears that Plots still does not support 3D Quiver. so I’m trying to see if there are any other packages such as PyPlot that has the facility to plot 3D Qui…

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## [Find dependent variables as GenericAffExpr](https://discourse.julialang.org/t/find-dependent-variables-as-genericaffexpr/46009)

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**Author:** [@umbe](https://discourse.julialang.org/u/umbe)\
**Replies:** 4\
**Last updated:** [September 4, 2020, 7:56am UTC](https://discourse.julialang.org/t/find-dependent-variables-as-genericaffexpr/46009 "2020-09-04T07:56:27Z")

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Hi everybody! I’m trying to find a way to obtain the dependent variables of a nonlinear system as GenericAffExpr, expressed as a function only of the independent variables of an optimization problem. To be more precise…

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## [Julia hangs while displaying an SMatrix](https://discourse.julialang.org/t/julia-hangs-while-displaying-an-smatrix/45918)

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**Author:** [@mzaffalon](https://discourse.julialang.org/u/mzaffalon)\
**Replies:** 3\
**Last updated:** [September 4, 2020, 7:37am UTC](https://discourse.julialang.org/t/julia-hangs-while-displaying-an-smatrix/45918 "2020-09-04T07:37:29Z")

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The following code hangs on Windows 10 and Julia 1.5.0 on two different computers: using StaticArrays struct Points{N,T\<:Number} p::SMatrix{3,N,T} end Points(x::Matrix{T}) where {T} = Points{size(x,2),T}(x) points…

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## [Error when installing registry](https://discourse.julialang.org/t/error-when-installing-registry/45999)

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**Author:** [@HerAdri](https://discourse.julialang.org/u/HerAdri)\
**Replies:** 5\
**Last updated:** [September 4, 2020, 6:13am UTC](https://discourse.julialang.org/t/error-when-installing-registry/45999 "2020-09-04T06:13:22Z")

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When you did the update, the following alert is displayed :. pkg\>up Installing known registries into C:\\Users\\hermesr\\.julia ERROR: SystemError: opening file “C:\\Users\\hermesr\\.julia\\registries\\General\\Registry.toml”:…

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## [How to use cases in docstring math mode?](https://discourse.julialang.org/t/how-to-use-cases-in-docstring-math-mode/46039)

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**Author:** [@jishnub](https://discourse.julialang.org/u/jishnub)\
**Replies:** 2\
**Last updated:** [September 4, 2020, 5:36am UTC](https://discourse.julialang.org/t/how-to-use-cases-in-docstring-math-mode/46039 "2020-09-04T05:36:03Z")

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I am using Documenter.jl to generate the documentation, and would like to use \\cases to define piecewise functions. Currently I am adding the equation to the docstring. Something like this doesn’t seem to render as latex…

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## [How to prevent memory build-up?](https://discourse.julialang.org/t/how-to-prevent-memory-build-up/45929)

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**Author:** [@adevaucorbeil](https://discourse.julialang.org/u/adevaucorbeil)\
**Replies:** 11\
**Last updated:** [September 4, 2020, 1:42am UTC](https://discourse.julialang.org/t/how-to-prevent-memory-build-up/45929 "2020-09-04T01:42:01Z")

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Hi there, I have a complex modeling code that involves a while loop which could be run a million times. In this loop, there are many, but some no-so complex mathematical operations involving SVectors and Arrays of SVect…

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## [Error evaluating sparse, analytical Jacobian from ModelingToolkit in DAE system](https://discourse.julialang.org/t/error-evaluating-sparse-analytical-jacobian-from-modelingtoolkit-in-dae-system/45764)

<div class="topic-metadata">

**Author:** [@DAEhelp](https://discourse.julialang.org/u/DAEhelp)\
**Replies:** 4\
**Last updated:** [September 4, 2020, 1:30am UTC](https://discourse.julialang.org/t/error-evaluating-sparse-analytical-jacobian-from-modelingtoolkit-in-dae-system/45764 "2020-09-04T01:30:25Z")

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I am having trouble with taking a sparse, analytical Jacobian generated in ModelingToolkit and passing it to my Sundials IDA solver. Here is an MWE adapted from a previous question. Running this segment of code with a p…

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## [Config information in Project.toml](https://discourse.julialang.org/t/config-information-in-project-toml/46016)

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**Author:** [@cstjean](https://discourse.julialang.org/u/cstjean)\
**Replies:** 3\
**Last updated:** [September 4, 2020, 12:14am UTC](https://discourse.julialang.org/t/config-information-in-project-toml/46016 "2020-09-04T00:14:53Z")

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Is it reasonable / possible to put config information in Project.toml? For instance, my\_app\_port = 8889. Are there facilities for parsing them? Or am I simply better off using environment variables somehow?

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## [Can't catch InitErrors?](https://discourse.julialang.org/t/cant-catch-initerrors/46033)

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**Author:** [@jwveysey](https://discourse.julialang.org/u/jwveysey)\
**Replies:** 0\
**Last updated:** [September 3, 2020, 11:35pm UTC](https://discourse.julialang.org/t/cant-catch-initerrors/46033 "2020-09-03T23:35:01Z")

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There’s probably an obvious answer to this question, but I can’t seem to find it. I have a package that loads another package with a using statement. The package that’s loaded has an init function that may error, so I’ve…

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