# Latest

**URL:** https://discourse.julialang.org/latest.md?page=740

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

**Page:** 741

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## [Why does add-assign to Ref{Float64} allocate?](https://discourse.julialang.org/t/why-does-add-assign-to-ref-float64-allocate/96767)

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**Author:** [@AlexanderNenninger](https://discourse.julialang.org/u/AlexanderNenninger)\
**Replies:** 3\
**Last updated:** [March 29, 2023, 12:50pm UTC](https://discourse.julialang.org/t/why-does-add-assign-to-ref-float64-allocate/96767 "2023-03-29T12:50:57Z")

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While optimizing some ODE code, I noticed that += on Ref{Float64} allocates, while .+= on a vector slice doen’t. Why is that? I wasn’t able to reproduce the effect without DifferentialEquations, but I feel like it shoul…

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## [My blink + interact code is not working after julia update](https://discourse.julialang.org/t/my-blink-interact-code-is-not-working-after-julia-update/96559)

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**Author:** [@Ludovic\_Dumoulin](https://discourse.julialang.org/u/Ludovic_Dumoulin)\
**Replies:** 15\
**Last updated:** [March 29, 2023, 11:33am UTC](https://discourse.julialang.org/t/my-blink-interact-code-is-not-working-after-julia-update/96559 "2023-03-29T11:33:57Z")

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Hello, I have a code that was working well before updating Julia to 1.8.5, but now I got an error that I don’t uderstand at all… The idea was to generate an interactive interface that can show a png/gif file depending …

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## [Pkg.jl question](https://discourse.julialang.org/t/pkg-jl-question/96759)

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**Author:** [@gitboy16](https://discourse.julialang.org/u/gitboy16)\
**Replies:** 4\
**Last updated:** [March 29, 2023, 10:39am UTC](https://discourse.julialang.org/t/pkg-jl-question/96759 "2023-03-29T10:39:51Z")

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Hi, Please see code below. julia\> pwd() "C:\\\\home" (@v1.8) pkg\> generate HelloWorld Generating project HelloWorld: HelloWorld\\Project.toml HelloWorld\\src\\HelloWorld.jl (@v1.8) pkg\> activate c:\\\\home\\\\Hello…

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## [How to set number of threads for VS Code?](https://discourse.julialang.org/t/how-to-set-number-of-threads-for-vs-code/47434)

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**Author:** [@DShiu](https://discourse.julialang.org/u/DShiu)\
**Replies:** 10\
**Last updated:** [March 29, 2023, 9:29am UTC](https://discourse.julialang.org/t/how-to-set-number-of-threads-for-vs-code/47434 "2023-03-29T09:29:59Z")

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There are quite a few topics about this question but I am still confused after reading them. I am using VS Code for Julia Version 1.5.0. Currently, The documentation (Multi-Threading · The Julia Language) says that we…

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## [MonteCarloTesting.jl — Statistical hypothesis testing via Monte Carlo simulations](https://discourse.julialang.org/t/montecarlotesting-jl-statistical-hypothesis-testing-via-monte-carlo-simulations/96762)

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**Author:** [@aplavin](https://discourse.julialang.org/u/aplavin)\
**Replies:** 0\
**Last updated:** [March 29, 2023, 9:02am UTC](https://discourse.julialang.org/t/montecarlotesting-jl-statistical-hypothesis-testing-via-monte-carlo-simulations/96762 "2023-03-29T09:02:41Z")

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MonteCarloTesting.jl (registered in General) performs hypothesis testing based on simulations, even when no analytic solutions are available. The only requirement is to be able to generate synthetic data under the null h…

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## [Create a \`Raster\` from OPeNDAP (netCDF)](https://discourse.julialang.org/t/create-a-raster-from-opendap-netcdf/96756)

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**Author:** [@ryofurue](https://discourse.julialang.org/u/ryofurue)\
**Replies:** 1\
**Last updated:** [March 29, 2023, 8:38am UTC](https://discourse.julialang.org/t/create-a-raster-from-opendap-netcdf/96756 "2023-03-29T08:38:43Z")

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The netCDF library has a builtin capability of lazily reading data from an OPeNDAP server as the following code demonstrates. I was wondering how to tell Raster to do the same. using NCDatasets: NCDataset using Rasters …

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## [How to provide a ca.cert file to HTTP.jl requests (I don't have a key file)](https://discourse.julialang.org/t/how-to-provide-a-ca-cert-file-to-http-jl-requests-i-dont-have-a-key-file/96757)

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**Author:** [@schlichtanders](https://discourse.julialang.org/u/schlichtanders)\
**Replies:** 0\
**Last updated:** [March 29, 2023, 8:27am UTC](https://discourse.julialang.org/t/how-to-provide-a-ca-cert-file-to-http-jl-requests-i-dont-have-a-key-file/96757 "2023-03-29T08:27:48Z")

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the documentation lists a couple of ssl configs which can be set a for a http request: SSL arguments: require\_ssl\_verification = NetworkOptions.verify\_host(host), pass MBEDTLS\_SSL\_VERIFY\_REQUIRED to the mbed TLS libr…

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## [Outer product of more than two vectors](https://discourse.julialang.org/t/outer-product-of-more-than-two-vectors/96310)

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**Author:** [@sylvaticus](https://discourse.julialang.org/u/sylvaticus)\
**Replies:** 16\
**Last updated:** [March 29, 2023, 7:57am UTC](https://discourse.julialang.org/t/outer-product-of-more-than-two-vectors/96310 "2023-03-29T07:57:17Z")

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Is there a built-in function for an outer product of more than two vectors, i.e.: julia\> a = \[0.2, 0.8\]; julia\> b = \[0.1,0.9\]; julia\> c = \[0.2,0.2,0.6\]; julia\> vs = \[a,b,c\]; # vector of vectors julia\> function ou…

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## [Join us at the Machine Learning ⇌ Science Colaboratory (Tübingen, Germany)](https://discourse.julialang.org/t/join-us-at-the-machine-learning-science-colaboratory-tubingen-germany/95440)

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**Author:** [@sethaxen](https://discourse.julialang.org/u/sethaxen)\
**Replies:** 1\
**Last updated:** [March 29, 2023, 7:51am UTC](https://discourse.julialang.org/t/join-us-at-the-machine-learning-science-colaboratory-tubingen-germany/95440 "2023-03-29T07:51:34Z")

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Are you passionate about probabilistic machine learning (ML), scientific datasets, and clean performant code? Would you like to feed your passion for science on cutting-edge research, from archaeology to particle physics…

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## [PlotlyJS: Select Browser to display html output](https://discourse.julialang.org/t/plotlyjs-select-browser-to-display-html-output/96277)

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**Author:** [@ellocco](https://discourse.julialang.org/u/ellocco)\
**Replies:** 7\
**Last updated:** [March 29, 2023, 7:02am UTC](https://discourse.julialang.org/t/plotlyjs-select-browser-to-display-html-output/96277 "2023-03-29T07:02:48Z")

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I have tried to find advise, how to specify the browser that is used to display the interactive html-ouput from PlotlyJS: I found some discussion how to change the default browser, but I would not like to change the the…

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## [Produced pie gauge chart using statisticalgraphics package](https://discourse.julialang.org/t/produced-pie-gauge-chart-using-statisticalgraphics-package/96753)

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**Author:** [@akshdfyehd](https://discourse.julialang.org/u/akshdfyehd)\
**Replies:** 0\
**Last updated:** [March 29, 2023, 6:17am UTC](https://discourse.julialang.org/t/produced-pie-gauge-chart-using-statisticalgraphics-package/96753 "2023-03-29T06:17:59Z")

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Hi, I have a dataset which looks like this: code to get this dataset: using InMemoryDatasets,DLMReader import Downloads data=Downloads.download("https://raw.githubusercontent.com/akshdfyehd/travel/main/Travel%20deta…

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## [Create a GroupedDataFrame by the relations of rows rather than the values of the rows in a column, e.g \`groupby\` consecutive dates?](https://discourse.julialang.org/t/create-a-groupeddataframe-by-the-relations-of-rows-rather-than-the-values-of-the-rows-in-a-column-e-g-groupby-consecutive-dates/96493)

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**Author:** [@phantom](https://discourse.julialang.org/u/phantom)\
**Replies:** 14\
**Last updated:** [March 29, 2023, 6:02am UTC](https://discourse.julialang.org/t/create-a-groupeddataframe-by-the-relations-of-rows-rather-than-the-values-of-the-rows-in-a-column-e-g-groupby-consecutive-dates/96493 "2023-03-29T06:02:02Z")

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Hi! hope all is well. Suppose there is the following DataFrame dr = collect(Date(2023,1,1):Day(1):Date(2023,1,10)); df = DataFrame(data = rand((1:10),7), dates=rand(dr,7)); sort!(df, :dates, rev = true) 7×2 DataF…

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## [Have HTTP.jl accept self-signed certificates for SSL](https://discourse.julialang.org/t/have-http-jl-accept-self-signed-certificates-for-ssl/96746)

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**Author:** [@screw\_dog](https://discourse.julialang.org/u/screw_dog)\
**Replies:** 1\
**Last updated:** [March 29, 2023, 5:51am UTC](https://discourse.julialang.org/t/have-http-jl-accept-self-signed-certificates-for-ssl/96746 "2023-03-29T05:51:09Z")

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Hi, I’m writing a package to wrap a REST API using HTTP.jl and want to use a simple Julia local server for testing. Since all the REST calls use HTTPS I’ve generated a self-signed certificate for this test server but, o…

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## [Discrete Optimization](https://discourse.julialang.org/t/discrete-optimization/96731)

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**Author:** [@Stuart\_Rogers](https://discourse.julialang.org/u/Stuart_Rogers)\
**Replies:** 5\
**Last updated:** [March 29, 2023, 5:28am UTC](https://discourse.julialang.org/t/discrete-optimization/96731 "2023-03-29T05:28:37Z")

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Is there a Julia optimization package that minimizes an objective function subject to constraints, where the unknowns are discrete (i.e., integer-valued), similar to MATLAB’s ga?

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## [Alternative to FluxOptTools?](https://discourse.julialang.org/t/alternative-to-fluxopttools/96747)

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**Author:** [@gnicolosi](https://discourse.julialang.org/u/gnicolosi)\
**Replies:** 2\
**Last updated:** [March 29, 2023, 5:13am UTC](https://discourse.julialang.org/t/alternative-to-fluxopttools/96747 "2023-03-29T05:13:44Z")

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Dear all, I have an optimization problem in which some of the functions are approximated by NNs, thus I am using Flux to represent them. The package FluxOptTools has allowed me to use Optim to optimize my “loss” functi…

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## [Questions on the DynamicalODE integrators](https://discourse.julialang.org/t/questions-on-the-dynamicalode-integrators/96721)

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**Author:** [@henry2004y](https://discourse.julialang.org/u/henry2004y)\
**Replies:** 5\
**Last updated:** [March 29, 2023, 2:44am UTC](https://discourse.julialang.org/t/questions-on-the-dynamicalode-integrators/96721 "2023-03-29T02:44:06Z")

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Hi! I have a question about the integrators in the differential equation community. The integrators for DynamicalODEProblem are listed in Dynamical, Hamiltonian, and 2nd Order ODE Solvers · DifferentialEquations.jl. Whi…

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## [How to create a Surface plot in Plot.jl from \`\`\`solve()\`\`\` data](https://discourse.julialang.org/t/how-to-create-a-surface-plot-in-plot-jl-from-solve-data/96684)

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**Author:** [@KZ-Spectra](https://discourse.julialang.org/u/KZ-Spectra)\
**Replies:** 4\
**Last updated:** [March 29, 2023, 1:44am UTC](https://discourse.julialang.org/t/how-to-create-a-surface-plot-in-plot-jl-from-solve-data/96684 "2023-03-29T01:44:11Z")

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MWE: N₁=5 γ=-1 #nonlinear term strength parameter g₁(u,p,t) = 1\*im\*(p\[1\]\*Tridiagonal(fill(1,N₁), fill(-2,N₁+1), fill(1,N₁))\*u + γ\*u.^3) vals=0.3\*ones(N₁+1) u0 =map(Complex,vals) tspan = (0.0,1.0) prob = ODEProblem(g…

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## [What is the deal with @kwdef](https://discourse.julialang.org/t/what-is-the-deal-with-kwdef/96733)

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**Author:** [@PetrKryslUCSD](https://discourse.julialang.org/u/PetrKryslUCSD)\
**Replies:** 2\
**Last updated:** [March 29, 2023, 12:32am UTC](https://discourse.julialang.org/t/what-is-the-deal-with-kwdef/96733 "2023-03-29T00:32:04Z")

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It is not in the manual, yet it seems to be ubiquitous in packages. What’s up with that? Edit: online search finally yielded something useful: What does @kwdef do? - #4 by j-fu I couldn’t find it before in this forum, …

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## [How do I do a plot in spherical coordinates?](https://discourse.julialang.org/t/how-do-i-do-a-plot-in-spherical-coordinates/96583)

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**Author:** [@rmfritz](https://discourse.julialang.org/u/rmfritz)\
**Replies:** 7\
**Last updated:** [March 28, 2023, 10:45pm UTC](https://discourse.julialang.org/t/how-do-i-do-a-plot-in-spherical-coordinates/96583 "2023-03-28T22:45:36Z")

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I either want to see a 3D surface or web of points. I suppose I can just take the 3D surface example as a model, but if possible, I would like to have angle axes. Is that possible with existing graphics libraries?

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## [What is the best way to calculate the numerical gradient of a matrix, representing multiple points in 3D space?](https://discourse.julialang.org/t/what-is-the-best-way-to-calculate-the-numerical-gradient-of-a-matrix-representing-multiple-points-in-3d-space/96727)

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**Author:** [@Dale\_James\_Black](https://discourse.julialang.org/u/Dale_James_Black)\
**Replies:** 10\
**Last updated:** [March 28, 2023, 10:04pm UTC](https://discourse.julialang.org/t/what-is-the-best-way-to-calculate-the-numerical-gradient-of-a-matrix-representing-multiple-points-in-3d-space/96727 "2023-03-28T22:04:10Z")

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Given a matrix, where each row represents a point in 3D space and each column represents the x, y, and z location. What is the recommended way to calculate the gradient at each point (at each row)? points = \[ 202 2…

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## [Is it possible to splat into ccall?](https://discourse.julialang.org/t/is-it-possible-to-splat-into-ccall/95761)

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**Author:** [@lmtzx9h4qqnt](https://discourse.julialang.org/u/lmtzx9h4qqnt)\
**Replies:** 31\
**Last updated:** [March 28, 2023, 7:15pm UTC](https://discourse.julialang.org/t/is-it-possible-to-splat-into-ccall/95761 "2023-03-28T19:15:52Z")

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As the title says – is it possible? A straightforward attempt doesn’t seem to work: julia\> ccall(:pow, Cdouble, (Cdouble, Cdouble), (2, 10)...) ERROR: syntax: more types than arguments for ccall around REPL\[65\]:1 The s…

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## [MethodError: no method matching\*Vector{Float64}](https://discourse.julialang.org/t/methoderror-no-method-matching-vector-float64/96720)

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**Author:** [@HamidLD](https://discourse.julialang.org/u/HamidLD)\
**Replies:** 7\
**Last updated:** [March 28, 2023, 6:43pm UTC](https://discourse.julialang.org/t/methoderror-no-method-matching-vector-float64/96720 "2023-03-28T18:43:07Z")

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Hi everyone, I know there are similar topics but I couldn’t fix my issue by reading them. I get this error: MethodError: no method matching \*(::Vector{Float64}, ::Vector{Float64}) And here is my code: function Qband…

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## [How can I convert a matrix of vectors to a 3d array?](https://discourse.julialang.org/t/how-can-i-convert-a-matrix-of-vectors-to-a-3d-array/96661)

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**Author:** [@kingoslo](https://discourse.julialang.org/u/kingoslo)\
**Replies:** 13\
**Last updated:** [March 28, 2023, 2:58pm UTC](https://discourse.julialang.org/t/how-can-i-convert-a-matrix-of-vectors-to-a-3d-array/96661 "2023-03-28T14:58:38Z")

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Hello there, I have a matrix of vectors. The type of the vactors are something non-default. I want to convert to a 3d array. I can see that similar questions have been asked for vectors of matrices, but those answers di…

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## [Julia \`Pkg\` seems to look in the wrong place when installing private package in Github CI](https://discourse.julialang.org/t/julia-pkg-seems-to-look-in-the-wrong-place-when-installing-private-package-in-github-ci/96694)

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**Author:** [@00krishna](https://discourse.julialang.org/u/00krishna)\
**Replies:** 8\
**Last updated:** [March 28, 2023, 2:48pm UTC](https://discourse.julialang.org/t/julia-pkg-seems-to-look-in-the-wrong-place-when-installing-private-package-in-github-ci/96694 "2023-03-28T14:48:15Z")

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I am using Github CI for package development. My package is private, and it has dependencies on some other private packages that I developed. While I can successfully clone the private dependency packages from github int…

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## [How to base64encode a BigInt?](https://discourse.julialang.org/t/how-to-base64encode-a-bigint/96668)

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**Author:** [@schlichtanders](https://discourse.julialang.org/u/schlichtanders)\
**Replies:** 4\
**Last updated:** [March 28, 2023, 2:13pm UTC](https://discourse.julialang.org/t/how-to-base64encode-a-bigint/96668 "2023-03-28T14:13:08Z")

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I was surprised finding that base64encode does not work for BigInt. Can someone help? julia\> using Base64 julia\> base64encode(BigInt(1234123)) ERROR: MethodError: no method matching write(::Base64EncodePipe, ::BigInt) C…

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## ["Very optimised" Julia code 50x slower than Python with compiled functions](https://discourse.julialang.org/t/very-optimised-julia-code-50x-slower-than-python-with-compiled-functions/96712)

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**Author:** [@StarecZosima](https://discourse.julialang.org/u/StarecZosima)\
**Replies:** 3\
**Last updated:** [March 28, 2023, 2:02pm UTC](https://discourse.julialang.org/t/very-optimised-julia-code-50x-slower-than-python-with-compiled-functions/96712 "2023-03-28T14:02:42Z")

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Hi All, I am doing some Monte Carlo computation using Python (compiling some functions to C++ using the Numba package). I thought I would see how Julia compares. As is good programming practice, I scraped some code fr…

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## [Relocatability of @\_\_DIR\_\_](https://discourse.julialang.org/t/relocatability-of-dir/96700)

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**Author:** [@sstroemer](https://discourse.julialang.org/u/sstroemer)\
**Replies:** 2\
**Last updated:** [March 28, 2023, 1:49pm UTC](https://discourse.julialang.org/t/relocatability-of-dir/96700 "2023-03-28T13:49:46Z")

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I am using the DIR macro in a function like: function foo() return joinpath(@\_\_DIR\_\_, "myfile.ext") end If function foo() gets precompiled using PackageCompiler.jl into a sysimage, the @\_\_DIR\_\_ is “hardcoded” into …

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## [ModelingToolkit & DifferentialEquations -- \`save\_idxs\`?](https://discourse.julialang.org/t/modelingtoolkit-differentialequations-save-idxs/96709)

<div class="topic-metadata">

**Author:** [@BLI](https://discourse.julialang.org/u/BLI)\
**Replies:** 1\
**Last updated:** [March 28, 2023, 1:15pm UTC](https://discourse.julialang.org/t/modelingtoolkit-differentialequations-save-idxs/96709 "2023-03-28T13:15:41Z")

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Coding my own models using DifferentialEquations solvers, it is possible to specify keyword save\_idxs to specify which variables are saved. What if I write the model using MTK instead? Will save\_idxs only work with a …

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## [Inverting a symmetric matrix is not faster than inverting a random one](https://discourse.julialang.org/t/inverting-a-symmetric-matrix-is-not-faster-than-inverting-a-random-one/96654)

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**Author:** [@tamasgal](https://discourse.julialang.org/u/tamasgal)\
**Replies:** 15\
**Last updated:** [March 27, 2023, 3:25pm UTC](https://discourse.julialang.org/t/inverting-a-symmetric-matrix-is-not-faster-than-inverting-a-random-one/96654 "2023-03-27T15:25:13Z")

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I thought that inverting a symmetric matrix would be faster, since there are optimised algorithms and I also saw that there is a method explicity for Symmetric, but maybe I am overlooking some trivial things, so please h…

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## [Package load speed: Windows vs Linux](https://discourse.julialang.org/t/package-load-speed-windows-vs-linux/93039)

<div class="topic-metadata">

**Author:** [@tfiers](https://discourse.julialang.org/u/tfiers)\
**Replies:** 24\
**Last updated:** [March 28, 2023, 12:21pm UTC](https://discourse.julialang.org/t/package-load-speed-windows-vs-linux/93039 "2023-03-28T12:21:21Z")

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I have a feeling that Julia package import times are significantly faster on Linux than on Windows. See e.g. this thread where: @giordano’s seven-year-old Linux laptop loads Unitful in 0.44 seconds my two-year-old Win…

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