# Latest

**URL:** https://discourse.julialang.org/latest.md?page=901

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

**Page:** 902

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## [XGBoost reduce overfitting | k-fold cross validation](https://discourse.julialang.org/t/xgboost-reduce-overfitting-k-fold-cross-validation/88423)

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**Author:** [@Seth16225](https://discourse.julialang.org/u/Seth16225)\
**Replies:** 1\
**Last updated:** [October 8, 2022, 12:25pm UTC](https://discourse.julialang.org/t/xgboost-reduce-overfitting-k-fold-cross-validation/88423 "2022-10-08T12:25:06Z")

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Hello, I’m pretty new to machine learning, and I was using XGBoost.jl Regression. I’m in the process of trying to reduce overfitting through k-fold cross validation. I came across the nfold\_cv function, and I was wonder…

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## [Callback at every 3 integrator steps in DIfferential equations.jl](https://discourse.julialang.org/t/callback-at-every-3-integrator-steps-in-differential-equations-jl/56775)

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**Author:** [@Sarthak\_Choudhury](https://discourse.julialang.org/u/Sarthak_Choudhury)\
**Replies:** 4\
**Last updated:** [October 8, 2022, 9:54am UTC](https://discourse.julialang.org/t/callback-at-every-3-integrator-steps-in-differential-equations-jl/56775 "2022-10-08T09:54:18Z")

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Hi there, This is a pretty basic question. I wanted to create a callback function which works after every 3 integrator steps. Since the time-steps are adaptive and hence unknown, is there any integrator options I could …

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## [Vectorised vs Devectorised Performance](https://discourse.julialang.org/t/vectorised-vs-devectorised-performance/88300)

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**Author:** [@StarecZosima](https://discourse.julialang.org/u/StarecZosima)\
**Replies:** 7\
**Last updated:** [October 8, 2022, 9:42am UTC](https://discourse.julialang.org/t/vectorised-vs-devectorised-performance/88300 "2022-10-08T09:42:05Z")

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Hi All, I was reading the interesting post Relationshop between vectorised and unvectorised code. The following two snippets are compared function vectorized() a = \[1.0, 1.0\] b = \[2.0, 2.0\] x = \[NaN, NaN\] …

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## [Parallel implementation is not very effective](https://discourse.julialang.org/t/parallel-implementation-is-not-very-effective/88323)

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**Author:** [@CarlosContrerasQ12](https://discourse.julialang.org/u/CarlosContrerasQ12)\
**Replies:** 19\
**Last updated:** [October 8, 2022, 8:28am UTC](https://discourse.julialang.org/t/parallel-implementation-is-not-very-effective/88323 "2022-10-08T08:28:37Z")

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Hi, I’m new to Julia and parallel programming and I’m having trouble with a parallel implementation. I need to assemble a matrix by calculating 10 individual blocks, each one taking approximately 18 seconds of computing …

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## [Vega-Lite plotting outside of data range with phantom data](https://discourse.julialang.org/t/vega-lite-plotting-outside-of-data-range-with-phantom-data/88426)

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**Author:** [@gtraeger](https://discourse.julialang.org/u/gtraeger)\
**Replies:** 5\
**Last updated:** [October 8, 2022, 5:34am UTC](https://discourse.julialang.org/t/vega-lite-plotting-outside-of-data-range-with-phantom-data/88426 "2022-10-08T05:34:12Z")

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I’m plotting temporal data from 1/1/2022 through 5/31/2022 by month. I’m getting bars from Jan through May which is ok. However, the plot is producing phantom data for Dec. I’ve checked six ways to Sunday and there is no…

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## [No method matching length() for any dot syntax operation involving a struct](https://discourse.julialang.org/t/no-method-matching-length-for-any-dot-syntax-operation-involving-a-struct/88425)

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**Author:** [@ivoytov](https://discourse.julialang.org/u/ivoytov)\
**Replies:** 6\
**Last updated:** [October 8, 2022, 5:27am UTC](https://discourse.julialang.org/t/no-method-matching-length-for-any-dot-syntax-operation-involving-a-struct/88425 "2022-10-08T05:27:55Z")

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I have experienced this problem a lot and it’s beyond frustrating. For some reason any dot syntax call that includes a struct fails. I can use map but is it possible to use dot syntax here? What am I missing? julia\> str…

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## [Constraints not being satisfied while using vector elements as rhs](https://discourse.julialang.org/t/constraints-not-being-satisfied-while-using-vector-elements-as-rhs/88294)

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**Author:** [@Gokhan\_Kof](https://discourse.julialang.org/u/Gokhan_Kof)\
**Replies:** 7\
**Last updated:** [October 8, 2022, 4:42am UTC](https://discourse.julialang.org/t/constraints-not-being-satisfied-while-using-vector-elements-as-rhs/88294 "2022-10-08T04:42:47Z")

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Hi, I am trying to solve the model below but the constraints are not being satisfied if I input a vector on the rhs (u\[j\] - 1). But, when I type it with hand (34, 28). It is being satisfied. ap.p 3 ap.n 5 ap.c 3×5×5 Ar…

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## [How to use a solution as starting point to run my NL model again after modifying something (e.g. a constraint)?](https://discourse.julialang.org/t/how-to-use-a-solution-as-starting-point-to-run-my-nl-model-again-after-modifying-something-e-g-a-constraint/88203)

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**Author:** [@Angel127](https://discourse.julialang.org/u/Angel127)\
**Replies:** 2\
**Last updated:** [October 8, 2022, 4:38am UTC](https://discourse.julialang.org/t/how-to-use-a-solution-as-starting-point-to-run-my-nl-model-again-after-modifying-something-e-g-a-constraint/88203 "2022-10-08T04:38:44Z")

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I have a NL model, and it finds a locally optimal solution after two hours. I would like to apply a nested for loop to use the epsilon constrained method. Then, on each iteration, some right-hand side coefficients will b…

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## [Model creation inside a loop](https://discourse.julialang.org/t/model-creation-inside-a-loop/88183)

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**Author:** [@Mariana](https://discourse.julialang.org/u/Mariana)\
**Replies:** 6\
**Last updated:** [October 8, 2022, 4:38am UTC](https://discourse.julialang.org/t/model-creation-inside-a-loop/88183 "2022-10-08T04:38:03Z")

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Hello! I’m using JuMP and Cbc solver to create an optimization model for each parameter p of a parameter set P, so basically, I have a code like this: for p in P model = create\_model(p) optimize! # Store resul…

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## [Partial tracing on a SDP @variable](https://discourse.julialang.org/t/partial-tracing-on-a-sdp-variable/88123)

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**Author:** [@danuzco](https://discourse.julialang.org/u/danuzco)\
**Replies:** 1\
**Last updated:** [October 8, 2022, 4:36am UTC](https://discourse.julialang.org/t/partial-tracing-on-a-sdp-variable/88123 "2022-10-08T04:36:32Z")

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I want to be able of partial tracing the X variable defined below : using ProxSDP, JuMP model = Model(with\_optimizer(ProxSDP.Optimizer, log\_verbose=false)) @variable(model, X\[1:N,1:N\], PSD) where N\>=1. I tried using Qu…

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## [Cannot \`convert\` an object of type Missing to an object of type Float64](https://discourse.julialang.org/t/cannot-convert-an-object-of-type-missing-to-an-object-of-type-float64/88421)

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**Author:** [@Leon6](https://discourse.julialang.org/u/Leon6)\
**Replies:** 3\
**Last updated:** [October 8, 2022, 12:53am UTC](https://discourse.julialang.org/t/cannot-convert-an-object-of-type-missing-to-an-object-of-type-float64/88421 "2022-10-08T00:53:55Z")

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I’m trying to read some data out of a NetCDF file and then convert it to Float64. Below is my code. Would you please help me address this error? My code: using NCDatasets ds1 = NCDataset("test.nc"); Var0 = ds1\["Variabl…

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## [Trouble plotting multiple spheres in GLMakie](https://discourse.julialang.org/t/trouble-plotting-multiple-spheres-in-glmakie/88387)

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**Author:** [@Mervyn\_Larrier](https://discourse.julialang.org/u/Mervyn_Larrier)\
**Replies:** 2\
**Last updated:** [October 7, 2022, 11:27pm UTC](https://discourse.julialang.org/t/trouble-plotting-multiple-spheres-in-glmakie/88387 "2022-10-07T23:27:09Z")

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I would like to plot a sphere inside another sphere. I’m using a wireframe to easily see the intersection in the spheres (if any exist), but I’m open to mesh solutions as well. The code compiles, but it won’t visualize; …

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## [Comparison of different fft-implementations](https://discourse.julialang.org/t/comparison-of-different-fft-implementations/86021)

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**Author:** [@ellocco](https://discourse.julialang.org/u/ellocco)\
**Replies:** 11\
**Last updated:** [October 7, 2022, 10:00pm UTC](https://discourse.julialang.org/t/comparison-of-different-fft-implementations/86021 "2022-10-07T22:00:26Z")

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Hi, I am struggling with fft-analysis of real-world data. Main objective are correct results. Currently I use two different fft-implementations: FFTW.fft() SciPy.fft.fft() The reason for this is that FFTW.fft() see…

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## [M1 MacBook, macOS/Julia 1.8 update issue: "cannot find libpython"](https://discourse.julialang.org/t/m1-macbook-macos-julia-1-8-update-issue-cannot-find-libpython/88419)

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**Author:** [@GlenHenshaw](https://discourse.julialang.org/u/GlenHenshaw)\
**Replies:** 2\
**Last updated:** [October 7, 2022, 9:31pm UTC](https://discourse.julialang.org/t/m1-macbook-macos-julia-1-8-update-issue-cannot-find-libpython/88419 "2022-10-07T21:31:35Z")

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Just upgraded to Julia 1.8.2, under macOS 12.6. python is installed via homebrew. I am getting the following error when running update: julia\> import Pkg julia\> Pkg.build("PyCall") Building Conda ─→ \`~/.julia/scrat…

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## [Pluto startup](https://discourse.julialang.org/t/pluto-startup/86805)

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**Author:** [@qwerty](https://discourse.julialang.org/u/qwerty)\
**Replies:** 0\
**Last updated:** [September 5, 2022, 2:40pm UTC](https://discourse.julialang.org/t/pluto-startup/86805 "2022-09-05T14:40:22Z")

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In 2022, what is the best method to speed up the startup of Pluto notebooks? If I precompile the packages I need and disable the pluto environment I get them to start instantly. However, Pluto takes almost a minute to s…

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## [How to do partial derivatives?](https://discourse.julialang.org/t/how-to-do-partial-derivatives/19869)

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**Author:** [@Lucy929](https://discourse.julialang.org/u/Lucy929)\
**Replies:** 14\
**Last updated:** [October 7, 2022, 7:16pm UTC](https://discourse.julialang.org/t/how-to-do-partial-derivatives/19869 "2022-10-07T19:16:41Z")

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I’m totally new in Julia. Now, I’m working on derivative. I found that ‘2nd derivatives’ (ex. function derivative\_sec\_fd(f,x)), but still couldn’t find how to do partial derivative… Could you tell me which command shoul…

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## [Feedback on a 2d spring simulation](https://discourse.julialang.org/t/feedback-on-a-2d-spring-simulation/88350)

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**Author:** [@maxkapur](https://discourse.julialang.org/u/maxkapur)\
**Replies:** 10\
**Last updated:** [October 7, 2022, 6:26pm UTC](https://discourse.julialang.org/t/feedback-on-a-2d-spring-simulation/88350 "2022-10-07T18:26:05Z")

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This post does not present a specific question or problem. I have working code—a tiny simulation of a dynamic system involving some springs in 2d space—and I am hoping for general feedback regarding code idiomaticity, pe…

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## [Nvidia AGX Orin](https://discourse.julialang.org/t/nvidia-agx-orin/84445)

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**Author:** [@johnh](https://discourse.julialang.org/u/johnh)\
**Replies:** 1\
**Last updated:** [October 7, 2022, 6:21pm UTC](https://discourse.julialang.org/t/nvidia-agx-orin/84445 "2022-10-07T18:21:26Z")

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I know I am behind the times,… but Oooo shiny… Ampere development kit

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## [Is there an error with the Sundials package (part of DifferentialEquations package)?](https://discourse.julialang.org/t/is-there-an-error-with-the-sundials-package-part-of-differentialequations-package/88341)

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**Author:** [@Kentaurkogen](https://discourse.julialang.org/u/Kentaurkogen)\
**Replies:** 10\
**Last updated:** [October 7, 2022, 4:29pm UTC](https://discourse.julialang.org/t/is-there-an-error-with-the-sundials-package-part-of-differentialequations-package/88341 "2022-10-07T16:29:18Z")

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Hello guys (this is my first topic) I’m trying to download the DIfferentialEquations package in order to solve some ODEs. However, I have a real difficulty downloading the sundials package which is installed during add …

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## [\[LinearSolve\] Inexact error in solving 4x4 linear system of equations](https://discourse.julialang.org/t/linearsolve-inexact-error-in-solving-4x4-linear-system-of-equations/88404)

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**Author:** [@TheLateKronos](https://discourse.julialang.org/u/TheLateKronos)\
**Replies:** 4\
**Last updated:** [October 7, 2022, 3:40pm UTC](https://discourse.julialang.org/t/linearsolve-inexact-error-in-solving-4x4-linear-system-of-equations/88404 "2022-10-07T15:40:06Z")

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I have this issue in solving a simple set of equations: julia\> using LinearSolve julia\> let A = \[1.0 0.0 -1.0 0.0 0.0 -3152.28 0.0 3152.28 0.…

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## [Ranking of elements of a vector](https://discourse.julialang.org/t/ranking-of-elements-of-a-vector/88293)

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**Author:** [@structural](https://discourse.julialang.org/u/structural)\
**Replies:** 13\
**Last updated:** [October 7, 2022, 3:17pm UTC](https://discourse.julialang.org/t/ranking-of-elements-of-a-vector/88293 "2022-10-07T15:17:59Z")

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I have a vector A. I need a vector RA which ranks each element of A. Is there a better way to do this than what I have below? A = \[4;2;5;1;6;7\] RA = sum((A .== sort(A)') .\* cumsum(ones(length(A)))', dims=2) display(\[A …

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## [Ncurses does not work](https://discourse.julialang.org/t/ncurses-does-not-work/88373)

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**Author:** [@whatsthecraic](https://discourse.julialang.org/u/whatsthecraic)\
**Replies:** 3\
**Last updated:** [October 7, 2022, 3:00pm UTC](https://discourse.julialang.org/t/ncurses-does-not-work/88373 "2022-10-07T15:00:22Z")

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Dear community, any idea how I should set up ncurses? # test-curses.jl using Ncurses\_jll ccall(("initscr", libncurses), Cvoid, ()) ccall(("getch", libncurses), Cint, ()) ccall(("endwin", libncurses), Cvoid, ()) output…

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## [JuliaCon Proceedings 2022](https://discourse.julialang.org/t/juliacon-proceedings-2022/84919)

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**Author:** [@mbesancon](https://discourse.julialang.org/u/mbesancon)\
**Replies:** 7\
**Last updated:** [October 7, 2022, 2:58pm UTC](https://discourse.julialang.org/t/juliacon-proceedings-2022/84919 "2022-10-07T14:58:53Z")

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Hello everyone, We hope you are all enjoying JuliaCon 2022! Like every year since the 2019 edition, the JuliaCon proceedings will be accepting extended abstract and full-length papers. The JuliaCon proceedings are an …

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## [WebIO Jupyter extension not working](https://discourse.julialang.org/t/webio-jupyter-extension-not-working/84340)

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**Author:** [@Aminath\_Shausan](https://discourse.julialang.org/u/Aminath_Shausan)\
**Replies:** 6\
**Last updated:** [October 7, 2022, 2:35pm UTC](https://discourse.julialang.org/t/webio-jupyter-extension-not-working/84340 "2022-10-07T14:35:44Z")

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Hi I am trying to replicate the interactive plots examples using Interact.jl package (Tutorial · Interact) on a Jupiter notebook. But running into problem with detecting WebIO. This is the first time I had to use WebIO …

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## [How to save vector of vectors with different dimensions?](https://discourse.julialang.org/t/how-to-save-vector-of-vectors-with-different-dimensions/88354)

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**Author:** [@elii17](https://discourse.julialang.org/u/elii17)\
**Replies:** 3\
**Last updated:** [October 7, 2022, 2:08pm UTC](https://discourse.julialang.org/t/how-to-save-vector-of-vectors-with-different-dimensions/88354 "2022-10-07T14:08:18Z")

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Hey ! I am looking for the optimal way of saving a vector of vectors in which each vector has different dimensions. The major problem is that I cannot save it as a df then get it as a CSV file… Thanks for your help !

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## [Julia simulations in the cloud - for dummies](https://discourse.julialang.org/t/julia-simulations-in-the-cloud-for-dummies/88395)

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**Author:** [@Nash](https://discourse.julialang.org/u/Nash)\
**Replies:** 1\
**Last updated:** [October 7, 2022, 1:24pm UTC](https://discourse.julialang.org/t/julia-simulations-in-the-cloud-for-dummies/88395 "2022-10-07T13:24:13Z")

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I am working through a simulation project that requires too much memory for my PC. Also, I need concurrency to cut down the time needed to complete all simulations. I have no experience with cloud computing and I hope s…

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## [How to Loop through excel files in a folder and update external links](https://discourse.julialang.org/t/how-to-loop-through-excel-files-in-a-folder-and-update-external-links/88385)

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**Author:** [@Dean\_Marshall](https://discourse.julialang.org/u/Dean_Marshall)\
**Replies:** 5\
**Last updated:** [October 7, 2022, 12:42pm UTC](https://discourse.julialang.org/t/how-to-loop-through-excel-files-in-a-folder-and-update-external-links/88385 "2022-10-07T12:42:43Z")

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Hi everyone, I am just starting out learning coding and essentially just use it to make ends meet at work at this stage, so apolagies in advance for being uneducated and illiterate in the matter. I use the below code in…

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## [Default length unit with PGFPlotsX and Plots](https://discourse.julialang.org/t/default-length-unit-with-pgfplotsx-and-plots/88367)

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**Author:** [@Gregstrq](https://discourse.julialang.org/u/Gregstrq)\
**Replies:** 3\
**Last updated:** [October 7, 2022, 12:40pm UTC](https://discourse.julialang.org/t/default-length-unit-with-pgfplotsx-and-plots/88367 "2022-10-07T12:40:56Z")

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I am using PGFPlotsX as a backend for Plots. I have specified the plot width as 800. After I saved the plot to pdf and inspected the properties, the width seems to be 194mm, which is around 550 pt. What are the default …

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## [Range behavior for Float32](https://discourse.julialang.org/t/range-behavior-for-float32/88393)

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**Author:** [@Iulian.Cioarca](https://discourse.julialang.org/u/Iulian.Cioarca)\
**Replies:** 1\
**Last updated:** [October 7, 2022, 11:57am UTC](https://discourse.julialang.org/t/range-behavior-for-float32/88393 "2022-10-07T11:57:29Z")

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I ran into the following issue on Julia 1.7.1: dt = 4.0e-9 l32 = 23\_849\_999 t = collect(0.0:dt:dt\*l32) # Vector{Float64} with 23850000 elements t0 = collect(LinRange(0.0, dt, l32+1)) # Vector{Float64} with 23850000 elem…

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## [Repartition data back and forward from one administrative division to another](https://discourse.julialang.org/t/repartition-data-back-and-forward-from-one-administrative-division-to-another/88389)

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**Author:** [@sylvaticus](https://discourse.julialang.org/u/sylvaticus)\
**Replies:** 1\
**Last updated:** [October 7, 2022, 11:55am UTC](https://discourse.julialang.org/t/repartition-data-back-and-forward-from-one-administrative-division-to-another/88389 "2022-10-07T11:55:17Z")

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I have some data relative to a certain administrative division, let’s say forest volumes per region. I need to translate this data in a second definition of “regions”, and sometimes I need to do the opposite. I have th…

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