# Latest

**URL:** https://discourse.julialang.org/latest.md?page=1452

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

**Page:** 1453

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## [Apply hessian of neural network to array](https://discourse.julialang.org/t/apply-hessian-of-neural-network-to-array/57602)

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**Author:** [@Sunny](https://discourse.julialang.org/u/Sunny)\
**Replies:** 2\
**Last updated:** [March 20, 2021, 2:35pm UTC](https://discourse.julialang.org/t/apply-hessian-of-neural-network-to-array/57602 "2021-03-20T14:35:37Z")

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I can simply take a hessian of some function in multiple points hess = x -\> (Zygote.hessian.(x-\>sum(x.^3), x)) hess(rand(2,3)) 2×3 Array{Float64,2}: 2.67795 3.8318 4.9022 0.216379 5.67439 4.96389 But I’m alway…

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## [How do I know which enviroment I am in?](https://discourse.julialang.org/t/how-do-i-know-which-enviroment-i-am-in/57600)

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**Author:** [@Ahmed\_Salih](https://discourse.julialang.org/u/Ahmed_Salih)\
**Replies:** 5\
**Last updated:** [March 20, 2021, 2:29pm UTC](https://discourse.julialang.org/t/how-do-i-know-which-enviroment-i-am-in/57600 "2021-03-20T14:29:59Z")

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Hi! I’ve been trying to follow the steps here: https://pkgdocs.julialang.org/v1/environments/ I am testing from the REPL. Basically I follow the steps and I see that I make a new project, which puts Pkg in the “MyProj…

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## [Crowdfunding Julia-based machine learning software](https://discourse.julialang.org/t/crowdfunding-julia-based-machine-learning-software/53190)

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**Author:** [@OMLA](https://discourse.julialang.org/u/OMLA)\
**Replies:** 7\
**Last updated:** [March 20, 2021, 2:08pm UTC](https://discourse.julialang.org/t/crowdfunding-julia-based-machine-learning-software/53190 "2021-03-20T14:08:03Z")

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Hello! We are a non-profit association developing open-source software based on Julia allowing to create, train and apply ML models through a graphical user interface without the need for programming or in-depth knowled…

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## [Algorithmic complexity of matrix multiplication in Julia](https://discourse.julialang.org/t/algorithmic-complexity-of-matrix-multiplication-in-julia/57468)

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**Author:** [@IlliaFaraji](https://discourse.julialang.org/u/IlliaFaraji)\
**Replies:** 10\
**Last updated:** [March 20, 2021, 12:57pm UTC](https://discourse.julialang.org/t/algorithmic-complexity-of-matrix-multiplication-in-julia/57468 "2021-03-20T12:57:09Z")

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This is a slightly odd question, but I am working on a project for which I would like to know the algorithmic complexity of matrix multiplication in Julia. i.e. if A, B are two dimensional n x n arrays stored in the usua…

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## [Difference between \`Union{Missing, Float64}\` and \`Float64?\`](https://discourse.julialang.org/t/difference-between-union-missing-float64-and-float64/57542)

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**Author:** [@alessio](https://discourse.julialang.org/u/alessio)\
**Replies:** 6\
**Last updated:** [March 20, 2021, 11:45am UTC](https://discourse.julialang.org/t/difference-between-union-missing-float64-and-float64/57542 "2021-03-20T11:45:10Z")

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I have a DataFrame that was created by importing a CSV. Then I applied several transformations. Now when I run describe on it I get some columns that report Union{Missing, Float64} as type and others report Float64?. Wh…

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## [Getting CartesianIndices to propagate](https://discourse.julialang.org/t/getting-cartesianindices-to-propagate/57315)

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**Author:** [@RainerHeintzmann](https://discourse.julialang.org/u/RainerHeintzmann)\
**Replies:** 8\
**Last updated:** [March 20, 2021, 11:43am UTC](https://discourse.julialang.org/t/getting-cartesianindices-to-propagate/57315 "2021-03-20T11:43:33Z")

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Julia (here 1.6RC1 on Windows 10) has a number of mechanism to calculate with positions inside an array such as ranges like (1:10) or generators or via CartesianIndices(x). Yet they all seem to not automatically propagat…

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## [2D graphics Library Recommendations](https://discourse.julialang.org/t/2d-graphics-library-recommendations/57202)

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**Author:** [@wali\_waqar](https://discourse.julialang.org/u/wali_waqar)\
**Replies:** 3\
**Last updated:** [March 20, 2021, 10:38am UTC](https://discourse.julialang.org/t/2d-graphics-library-recommendations/57202 "2021-03-20T10:38:13Z")

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Hi, I am making a browser engine in Julia, could you please recommend a drawing/graphics library to use?

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## [Need help understanding performance hit of Arrays](https://discourse.julialang.org/t/need-help-understanding-performance-hit-of-arrays/57450)

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**Author:** [@nandoconde](https://discourse.julialang.org/u/nandoconde)\
**Replies:** 3\
**Last updated:** [March 20, 2021, 10:03am UTC](https://discourse.julialang.org/t/need-help-understanding-performance-hit-of-arrays/57450 "2021-03-20T10:03:03Z")

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Intro Hello! I have been using Julia regularly for some months and I am starting to have a good mental map of the way Julia works internally, meaning, which operations can be optimized by the compiler and how to write le…

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## [Jobs based on Julia Software](https://discourse.julialang.org/t/jobs-based-on-julia-software/57574)

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**Author:** [@Manisha\_07](https://discourse.julialang.org/u/Manisha_07)\
**Replies:** 3\
**Last updated:** [March 20, 2021, 8:11am UTC](https://discourse.julialang.org/t/jobs-based-on-julia-software/57574 "2021-03-20T08:11:27Z")

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Hello Zussamen Presently I am studying masters in Mechatrnics.This sem I have choosen to do prject on control theory for which iam using Julia software. I wanted to know how is the job market for this software and which…

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## [How to constraint a outer type of a variable in a struct to be the same, but allow the inner type to be different?](https://discourse.julialang.org/t/how-to-constraint-a-outer-type-of-a-variable-in-a-struct-to-be-the-same-but-allow-the-inner-type-to-be-different/57565)

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**Author:** [@zsoerenm](https://discourse.julialang.org/u/zsoerenm)\
**Replies:** 2\
**Last updated:** [March 20, 2021, 8:03am UTC](https://discourse.julialang.org/t/how-to-constraint-a-outer-type-of-a-variable-in-a-struct-to-be-the-same-but-allow-the-inner-type-to-be-different/57565 "2021-03-20T08:03:59Z")

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How to constraint a outer type of a variable in a struct to be the same, but allow the inner type to be different? e.g. struct Foo{A\<:Union{\<:AbstractMatrix, Cholesky}} a::A b::A end In this example a & b can …

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## [Package definition](https://discourse.julialang.org/t/package-definition/57563)

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**Author:** [@roryh](https://discourse.julialang.org/u/roryh)\
**Replies:** 1\
**Last updated:** [March 20, 2021, 7:53am UTC](https://discourse.julialang.org/t/package-definition/57563 "2021-03-20T07:53:57Z")

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I’ve recently moved from c++ and python to julia as the perfect one stop shop for all my simulation needs. One thing I struggled with for quite a bit and seems others do as well is the concept of packages and projects. T…

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## [Save figures as pdf](https://discourse.julialang.org/t/save-figures-as-pdf/57503)

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**Author:** [@Rasoul\_Jafarzadeh](https://discourse.julialang.org/u/Rasoul_Jafarzadeh)\
**Replies:** 4\
**Last updated:** [March 20, 2021, 7:33am UTC](https://discourse.julialang.org/t/save-figures-as-pdf/57503 "2021-03-20T07:33:02Z")

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In my code, I have lots of figuers and I want them to save as pdf. I did it but all plots saved in one page. How can I save them in some pages?

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## [Graph with tuple vertices?](https://discourse.julialang.org/t/graph-with-tuple-vertices/57585)

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**Author:** [@DevJac](https://discourse.julialang.org/u/DevJac)\
**Replies:** 1\
**Last updated:** [March 20, 2021, 5:41am UTC](https://discourse.julialang.org/t/graph-with-tuple-vertices/57585 "2021-03-20T05:41:14Z")

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I need to work with a graph where the vertices are tuples. All the graph libraries I’ve seen in Julia expect the graph vertices to be integers. Any suggestions?

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## [Want to generate samples with all items being sampled the same number of times?](https://discourse.julialang.org/t/want-to-generate-samples-with-all-items-being-sampled-the-same-number-of-times/57351)

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**Author:** [@DevJac](https://discourse.julialang.org/u/DevJac)\
**Replies:** 4\
**Last updated:** [March 20, 2021, 4:05am UTC](https://discourse.julialang.org/t/want-to-generate-samples-with-all-items-being-sampled-the-same-number-of-times/57351 "2021-03-20T04:05:24Z")

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Is there any library that can help me generate random “batches” of data such that every item appears in the same number of batches (with the exception that some items may appear one more time than other items)?

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## [How to call parallel fortran code from Julia correctly?](https://discourse.julialang.org/t/how-to-call-parallel-fortran-code-from-julia-correctly/57583)

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**Author:** [@DerongXu](https://discourse.julialang.org/u/DerongXu)\
**Replies:** 0\
**Last updated:** [March 20, 2021, 2:08am UTC](https://discourse.julialang.org/t/how-to-call-parallel-fortran-code-from-julia-correctly/57583 "2021-03-20T02:08:38Z")

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Hi All, I am new to Julia. I would like to call the MPI FORTRAN code in Julia. However, when the Fortran code involve MPI\_Init, I cannot run my code correctly. A minimum demo is shown below. -------------Fortran code: …

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## [Stff System](https://discourse.julialang.org/t/stff-system/57569)

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**Author:** [@Manisha\_07](https://discourse.julialang.org/u/Manisha_07)\
**Replies:** 2\
**Last updated:** [March 19, 2021, 10:52pm UTC](https://discourse.julialang.org/t/stff-system/57569 "2021-03-19T22:52:04Z")

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I am very new to Julia While solving ODE i have come across Stiff system Wat does the Stiff system means.

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## [Update Julia Package in Jupyter notebook](https://discourse.julialang.org/t/update-julia-package-in-jupyter-notebook/57414)

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**Author:** [@Manisha\_07](https://discourse.julialang.org/u/Manisha_07)\
**Replies:** 5\
**Last updated:** [March 19, 2021, 10:49pm UTC](https://discourse.julialang.org/t/update-julia-package-in-jupyter-notebook/57414 "2021-03-19T22:49:48Z")

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Hello I have added ODE package in Julia and i tried to work in jupyter notebook env but still iam getting the error as install ODE How would i resolve it. Pls help me

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## [No method matching zero(::Type{Array{Float64,2}})](https://discourse.julialang.org/t/no-method-matching-zero-type-array-float64-2/57538)

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**Author:** [@Shazman](https://discourse.julialang.org/u/Shazman)\
**Replies:** 13\
**Last updated:** [March 19, 2021, 9:29pm UTC](https://discourse.julialang.org/t/no-method-matching-zero-type-array-float64-2/57538 "2021-03-19T21:29:20Z")

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Hi, I am using Julia to solve the equation below, where XS is a large matrix and XT is a transpose version of XS. LamI is a diagonal matrix and RHS is a vector. using DelimitedFiles using LinearAlgebra XS = readdl…

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## [Get suffix from Vector of Vectors](https://discourse.julialang.org/t/get-suffix-from-vector-of-vectors/57489)

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**Author:** [@Sleepy](https://discourse.julialang.org/u/Sleepy)\
**Replies:** 2\
**Last updated:** [March 19, 2021, 8:36pm UTC](https://discourse.julialang.org/t/get-suffix-from-vector-of-vectors/57489 "2021-03-19T20:36:12Z")

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Given is a vector of vectors s = \[\[3, 2, 1, 1, 1\],\[3, 1, 2, 1, 3\]\] where all vectors have the same length and an index vector i = \[3,4\] Is there an easy way to get the subvectors of s, starting at index i.e. 3 to end…

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## [Using jldoctest across Julia versions](https://discourse.julialang.org/t/using-jldoctest-across-julia-versions/57562)

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**Author:** [@nben](https://discourse.julialang.org/u/nben)\
**Replies:** 1\
**Last updated:** [March 19, 2021, 8:35pm UTC](https://discourse.julialang.org/t/using-jldoctest-across-julia-versions/57562 "2021-03-19T20:35:52Z")

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I am developing a library called Air that includes persistent collection types. (I don’t think this context is very important, but the link is included in case it helps.) As part of this I have a large number of jldoctes…

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## [Poisson changepoint model: UK Coal Mining Disasters](https://discourse.julialang.org/t/poisson-changepoint-model-uk-coal-mining-disasters/57470)

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**Author:** [@gsinha](https://discourse.julialang.org/u/gsinha)\
**Replies:** 10\
**Last updated:** [March 19, 2021, 8:32pm UTC](https://discourse.julialang.org/t/poisson-changepoint-model-uk-coal-mining-disasters/57470 "2021-03-19T20:32:36Z")

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Hi: In an effort to learn Turing, I set out to replicate the UK Coal Mining disasters example. I think I’ve managed to successfully replicate the results - this is what I did. using Turing using Distributions using Dis…

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## [Exported function not available](https://discourse.julialang.org/t/exported-function-not-available/57535)

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**Author:** [@erlebach1](https://discourse.julialang.org/u/erlebach1)\
**Replies:** 8\
**Last updated:** [March 19, 2021, 7:23pm UTC](https://discourse.julialang.org/t/exported-function-not-available/57535 "2021-03-19T19:23:09Z")

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Hi, I am relatively new to Julia and came across a strange problem using ForneyLab, but which be more general. After typing using ForneyLab in the REPL of Atom, I confirm that I have access to InferenceAlgorithm, c…

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## [Struct variables explicit setting](https://discourse.julialang.org/t/struct-variables-explicit-setting/57396)

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**Author:** [@Ribeiro](https://discourse.julialang.org/u/Ribeiro)\
**Replies:** 30\
**Last updated:** [March 19, 2021, 7:21pm UTC](https://discourse.julialang.org/t/struct-variables-explicit-setting/57396 "2021-03-19T19:21:08Z")

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Hi! I know how to do this: struct a a1 a2 a3 end b=a(1,2,3) I was wondering if there’s a way to do this in a more explicit way. Something like: b=a(a1=1,a2=2,a3=3). The reason would be readabilit…

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## [Fast Hessian size increase](https://discourse.julialang.org/t/fast-hessian-size-increase/57560)

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**Author:** [@Sunny](https://discourse.julialang.org/u/Sunny)\
**Replies:** 6\
**Last updated:** [March 19, 2021, 6:58pm UTC](https://discourse.julialang.org/t/fast-hessian-size-increase/57560 "2021-03-19T18:58:15Z")

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I’d like to compute the Hessian for array values and to get some array with dimension (2,2) but instead I got this julia\> hessian(x -\> sum(x.^3), \[1 2; 3 4\]) # uses linear indexing of x 4×4 Array{$Int,2}: 6 0 0 …

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## [Why is SUM always used in differentiation?](https://discourse.julialang.org/t/why-is-sum-always-used-in-differentiation/57559)

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**Author:** [@Sunny](https://discourse.julialang.org/u/Sunny)\
**Replies:** 3\
**Last updated:** [March 19, 2021, 6:54pm UTC](https://discourse.julialang.org/t/why-is-sum-always-used-in-differentiation/57559 "2021-03-19T18:54:55Z")

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I’ve seen a lot of examples where the output of a NN or any function during the differentiation is preprocessed with sum operator. For example this: julia\> hessian(x -\> sum(x.^3), \[1 2; 3 4\]) # uses linear indexing of …

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## [Any risk in changing Github repo name from \`MyProject\` to \`MyProject.jl\`?](https://discourse.julialang.org/t/any-risk-in-changing-github-repo-name-from-myproject-to-myproject-jl/54598)

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**Author:** [@maxkapur](https://discourse.julialang.org/u/maxkapur)\
**Replies:** 4\
**Last updated:** [March 19, 2021, 5:07pm UTC](https://discourse.julialang.org/t/any-risk-in-changing-github-repo-name-from-myproject-to-myproject-jl/54598 "2021-03-19T17:07:28Z")

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I recently had a package accepted for auto-merge into the General registry (pending the three-day waiting period). It is named MyProject, the main code is at src/MyProject.jl, and the Project.toml file says name = "MyPro…

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## [New Julia Package for F16 Aircraft Model](https://discourse.julialang.org/t/new-julia-package-for-f16-aircraft-model/57323)

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**Author:** [@raktim](https://discourse.julialang.org/u/raktim)\
**Replies:** 12\
**Last updated:** [March 19, 2021, 4:52pm UTC](https://discourse.julialang.org/t/new-julia-package-for-f16-aircraft-model/57323 "2021-03-19T16:52:57Z")

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F16Model.jl is a Julia package for a nonlinear model of the F16 aircraft. The aerodynamics included in this model come from the NASA Technical Report 1538, Simulator Study of Stall/Post-Stall Characteristics of a Fighter…

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## [Threads and stdlib Random](https://discourse.julialang.org/t/threads-and-stdlib-random/57539)

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**Author:** [@evanfields](https://discourse.julialang.org/u/evanfields)\
**Replies:** 4\
**Last updated:** [March 19, 2021, 4:27pm UTC](https://discourse.julialang.org/t/threads-and-stdlib-random/57539 "2021-03-19T16:27:25Z")

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What’s the state of the Random stdlib and thread safety? I thought I remembered some notes on this from several Julia releases back, but the Random docs have almost nothing on the topic. The only reference to threads is …

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## [Even more bare baremodule](https://discourse.julialang.org/t/even-more-bare-baremodule/56156)

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**Author:** [@Mason](https://discourse.julialang.org/u/Mason)\
**Replies:** 8\
**Last updated:** [March 19, 2021, 4:25pm UTC](https://discourse.julialang.org/t/even-more-bare-baremodule/56156 "2021-03-19T16:25:22Z")

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Is there a way to create a baremodule that doesn’t import Core? Currently, baremodule does using Core, so it’s namespace really isn’t as bare as one might like because Core exports 97 names: julia\> names(Core) 97-elemen…

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## [Is there a power flow formulation that considers branches power transfer limit in PowerModels.jl?](https://discourse.julialang.org/t/is-there-a-power-flow-formulation-that-considers-branches-power-transfer-limit-in-powermodels-jl/57548)

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**Author:** [@RaulRib](https://discourse.julialang.org/u/RaulRib)\
**Replies:** 2\
**Last updated:** [March 19, 2021, 3:48pm UTC](https://discourse.julialang.org/t/is-there-a-power-flow-formulation-that-considers-branches-power-transfer-limit-in-powermodels-jl/57548 "2021-03-19T15:48:56Z")

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Hello, I am working on a project where I investigate the behavior of power systems with congested lines.When running run\_ac\_pf or run\_dc\_pf, I notice that some branches resulting power flow exceed their limit. Searching…

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