# Specific Domains

**URL:** https://discourse.julialang.org/c/domain/10.md?no_subcategories=false&page=424

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**Page:** 425

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## [Why isn't \`i\` defined inside this while?](https://discourse.julialang.org/t/why-isnt-i-defined-inside-this-while/45882)

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**Author:** [@Somayeh\_Esmaeili](https://discourse.julialang.org/u/Somayeh_Esmaeili)\
**Replies:** 4\
**Last updated:** [September 1, 2020, 10:08am UTC](https://discourse.julialang.org/t/why-isnt-i-defined-inside-this-while/45882 "2020-09-01T10:08:14Z")

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would you please help me why i cant be known inside this while as following in julia v1+? W=(\[1.0825998948767477 9.448347129060197 972.5335271289529; 165.861582812015 4.563134610834678 1.0293311999771995\], 0) i=1; k=siz…

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## [Flux and cpu cores](https://discourse.julialang.org/t/flux-and-cpu-cores/45318)

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**Author:** [@johnbb](https://discourse.julialang.org/u/johnbb)\
**Replies:** 6\
**Last updated:** [September 1, 2020, 9:29am UTC](https://discourse.julialang.org/t/flux-and-cpu-cores/45318 "2020-09-01T09:29:57Z")

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When I run the following code using Flux n = 100\_000 p = 50 x = rand(Float32, p, n) y = rand(Float32, n) trdata = Flux.Data.DataLoader(x, y, batchsize=100) m = Chain(Dense(p, 100), Dense(100,100), Dense(100,1)) loss…

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## [Vertical errors for historgrams](https://discourse.julialang.org/t/vertical-errors-for-historgrams/45881)

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**Author:** [@misha\_mikhasenko](https://discourse.julialang.org/u/misha_mikhasenko)\
**Replies:** 2\
**Last updated:** [September 1, 2020, 9:27am UTC](https://discourse.julialang.org/t/vertical-errors-for-historgrams/45881 "2020-09-01T09:27:06Z")

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In my field of research (HEP), the vertical errors for the histograms are widely used. Usually, they are calculated assuming narrow bins and Poisson distribution for the number of entries, i.e. the error is sqrt(Nentri…

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## [Models precompilation and general modelling platform architecture](https://discourse.julialang.org/t/models-precompilation-and-general-modelling-platform-architecture/45599)

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**Author:** [@ivborissov](https://discourse.julialang.org/u/ivborissov)\
**Replies:** 11\
**Last updated:** [September 1, 2020, 9:01am UTC](https://discourse.julialang.org/t/models-precompilation-and-general-modelling-platform-architecture/45599 "2020-09-01T09:01:45Z")

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Hi, could you please help me with the following workflow question. Let’s say I have a simulation platform as julia package X and a number of models as julia .jl files. I would like say using X then precompile and upload…

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## [Using ModelingToolkit to invert a symbolic matrix](https://discourse.julialang.org/t/using-modelingtoolkit-to-invert-a-symbolic-matrix/45642)

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**Author:** [@Bruno\_Mendes](https://discourse.julialang.org/u/Bruno_Mendes)\
**Replies:** 10\
**Last updated:** [August 31, 2020, 9:31pm UTC](https://discourse.julialang.org/t/using-modelingtoolkit-to-invert-a-symbolic-matrix/45642 "2020-08-31T21:31:14Z")

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Hi. I’m trying to invert a mass matrix with the purpose of decoupling the second order derivatives of a dynamic system, using ModelingToolkit.jl. The matrix is something like this: In Julia, the elements of this matr…

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## [Faster small CUDA memory transfers (UnifiedMem?)](https://discourse.julialang.org/t/faster-small-cuda-memory-transfers-unifiedmem/45850)

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**Author:** [@Alex\_Ellison](https://discourse.julialang.org/u/Alex_Ellison)\
**Replies:** 2\
**Last updated:** [August 31, 2020, 8:14pm UTC](https://discourse.julialang.org/t/faster-small-cuda-memory-transfers-unifiedmem/45850 "2020-08-31T20:14:21Z")

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Hey, I’m trying to write a program which launches many kernels, but the launches depend on results of earlier kernels. Sometimes the result means a kernel should not be launched at all. They can be distributed across ma…

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## [Table views](https://discourse.julialang.org/t/table-views/45834)

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**Author:** [@juliohm](https://discourse.julialang.org/u/juliohm)\
**Replies:** 7\
**Last updated:** [August 31, 2020, 5:37pm UTC](https://discourse.julialang.org/t/table-views/45834 "2020-08-31T17:37:24Z")

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There are various efforts in the tables ecosystem to create a common language for table operations: Query.jl DataKnots.jl TableOperations.jl Volcanito.jl I couldn’t find in any of these efforts an operation to select …

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## [Make plots in separate windows](https://discourse.julialang.org/t/make-plots-in-separate-windows/45815)

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**Author:** [@Sanji\_Vinsmoke](https://discourse.julialang.org/u/Sanji_Vinsmoke)\
**Replies:** 7\
**Last updated:** [August 31, 2020, 8:01am UTC](https://discourse.julialang.org/t/make-plots-in-separate-windows/45815 "2020-08-31T08:01:22Z")

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I want to plot different arrays and show the plot in separate windows when I run the julia script from the REPL using the include("\<name\>.jl") I searched it on the internet and I got to know about reuse = false, but whe…

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## [LightGraphs: get all of the the shortest paths between 2 points?](https://discourse.julialang.org/t/lightgraphs-get-all-of-the-the-shortest-paths-between-2-points/28775)

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**Author:** [@wherrera](https://discourse.julialang.org/u/wherrera)\
**Replies:** 1\
**Last updated:** [August 30, 2020, 8:46pm UTC](https://discourse.julialang.org/t/lightgraphs-get-all-of-the-the-shortest-paths-between-2-points/28775 "2020-08-30T20:46:33Z")

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Consider using LightGraphs g = SimpleDiGraph(7) add\_edge!(g, 1, 2) add\_edge!(g, 2, 3) add\_edge!(g, 4, 5) add\_edge!(g, 5, 3) add\_edge!(g, 1, 5) add\_edge!(g, 6, 7) add\_edge!(g, 7, 3) add\_edge!(g, 1, 7) p = dijkstra\_shor…

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## [Error building CPLEX](https://discourse.julialang.org/t/error-building-cplex/45798)

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**Author:** [@Glaucio](https://discourse.julialang.org/u/Glaucio)\
**Replies:** 1\
**Last updated:** [August 30, 2020, 8:29pm UTC](https://discourse.julialang.org/t/error-building-cplex/45798 "2020-08-30T20:29:52Z")

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me ajudem

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## [How to sample a clustered group from a DataFrame?](https://discourse.julialang.org/t/how-to-sample-a-clustered-group-from-a-dataframe/45777)

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**Author:** [@Jaepil\_Lee](https://discourse.julialang.org/u/Jaepil_Lee)\
**Replies:** 2\
**Last updated:** [August 30, 2020, 3:37pm UTC](https://discourse.julialang.org/t/how-to-sample-a-clustered-group-from-a-dataframe/45777 "2020-08-30T15:37:46Z")

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Hello Julia users! I have been trying to implement a Bootstrap from a panel data, stored in DataFrames. I think I got it working, but I am doing it in a super inefficient way. For example, as soon as I draw a vector of…

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## [Plotting coefplot](https://discourse.julialang.org/t/plotting-coefplot/45779)

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**Author:** [@qwerytyui1234](https://discourse.julialang.org/u/qwerytyui1234)\
**Replies:** 4\
**Last updated:** [August 30, 2020, 3:25pm UTC](https://discourse.julialang.org/t/plotting-coefplot/45779 "2020-08-30T15:25:26Z")

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Hello everyone, I am trying to plot something like this (attached below), but I am not able to find how to plot this particular way. How would you plot something like this? Thanks in advance.

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## [Approximating via step function](https://discourse.julialang.org/t/approximating-via-step-function/43577)

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**Author:** [@danicaratelli](https://discourse.julialang.org/u/danicaratelli)\
**Replies:** 2\
**Last updated:** [August 30, 2020, 6:53am UTC](https://discourse.julialang.org/t/approximating-via-step-function/43577 "2020-08-30T06:53:10Z")

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Hello, I was wondering whether anyone knows of a package/function that approximates a function with a step function. As an example, below in blue is the data I am trying to approximate, in red is my wanted output (a ste…

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## [How to create a loss function with 3 inputs in Flux?](https://discourse.julialang.org/t/how-to-create-a-loss-function-with-3-inputs-in-flux/45755)

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**Author:** [@DeepQ](https://discourse.julialang.org/u/DeepQ)\
**Replies:** 2\
**Last updated:** [August 30, 2020, 3:51am UTC](https://discourse.julialang.org/t/how-to-create-a-loss-function-with-3-inputs-in-flux/45755 "2020-08-30T03:51:26Z")

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How could I create a loss function with 3 inputs like loss(w,x,y)? Could someone show me an example?

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## [Recommended Saves and Loads of DataFrame : JLD, CSV, etc](https://discourse.julialang.org/t/recommended-saves-and-loads-of-dataframe-jld-csv-etc/9074)

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**Author:** [@ivo\_welch](https://discourse.julialang.org/u/ivo_welch)\
**Replies:** 8\
**Last updated:** [August 30, 2020, 3:36am UTC](https://discourse.julialang.org/t/recommended-saves-and-loads-of-dataframe-jld-csv-etc/9074 "2020-08-30T03:36:22Z")

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I am using 0.6.2, but am planning to move to 1.0 when available. I read in an earlier discussion (/suggested-formats-for-saving-and-serialization/3230) that JLD has not been working. I have tried to save() some datafra…

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## [Proposal for automatic diagram creation system for Julia - Inspiration Penrose](https://discourse.julialang.org/t/proposal-for-automatic-diagram-creation-system-for-julia-inspiration-penrose/45750)

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**Author:** [@bradeneliason](https://discourse.julialang.org/u/bradeneliason)\
**Replies:** 1\
**Last updated:** [August 29, 2020, 6:31pm UTC](https://discourse.julialang.org/t/proposal-for-automatic-diagram-creation-system-for-julia-inspiration-penrose/45750 "2020-08-29T18:31:59Z")

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Penrose is a system under development which automatically creates math diagrams that would be suitable for a textbook directly from abstract mathematical specification. A simple example is creating Venn diagrams from set…

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## [Working with dictionaries in @variables and @constraints](https://discourse.julialang.org/t/working-with-dictionaries-in-variables-and-constraints/45726)

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**Author:** [@sogrbilja](https://discourse.julialang.org/u/sogrbilja)\
**Replies:** 2\
**Last updated:** [August 29, 2020, 2:48pm UTC](https://discourse.julialang.org/t/working-with-dictionaries-in-variables-and-constraints/45726 "2020-08-29T14:48:43Z")

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I wonder if it is possible to work with Dict in @variables and @constraints like this: \_ORDER\_PRODUCTS and UNITS are Dict @constraint(premex, PRODAMOUNTint\_upper\[op in \_ORDER\_PRODUCTS, u in UNITS, t in TIME\], …

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## [Expressions for partial derivatives using AD tools](https://discourse.julialang.org/t/expressions-for-partial-derivatives-using-ad-tools/45741)

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**Author:** [@JLHTM](https://discourse.julialang.org/u/JLHTM)\
**Replies:** 2\
**Last updated:** [August 29, 2020, 1:53pm UTC](https://discourse.julialang.org/t/expressions-for-partial-derivatives-using-ad-tools/45741 "2020-08-29T13:53:51Z")

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I have two bivariate functions (more generally, n n-variable functions) f\_1(x\_1,x\_2) and f\_2(x\_1,x\_2). I need to solve the following system of equations: \\frac{\\partial f\_1}{\\partial x\_1} = 0 and \\frac{\\partial f\_2}{\\par…

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## [ERROR: MethodError: no method matching Model](https://discourse.julialang.org/t/error-methoderror-no-method-matching-model/45699)

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**Author:** [@cotepascal76](https://discourse.julialang.org/u/cotepascal76)\
**Replies:** 2\
**Last updated:** [August 29, 2020, 10:34am UTC](https://discourse.julialang.org/t/error-methoderror-no-method-matching-model/45699 "2020-08-29T10:34:26Z")

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Hello, I’m new in Julia and JuMP and I just tried to install and test JuMP but I got this error (with all solvers that I tested): julia\> Model(Gurobi.Optimizer) ERROR: MethodError: no method matching Model(::Type{Gurob…

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## [Why does Zygote produce a wrong derivative?](https://discourse.julialang.org/t/why-does-zygote-produce-a-wrong-derivative/45724)

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**Author:** [@joachimbrand1](https://discourse.julialang.org/u/joachimbrand1)\
**Replies:** 5\
**Last updated:** [August 29, 2020, 9:06am UTC](https://discourse.julialang.org/t/why-does-zygote-produce-a-wrong-derivative/45724 "2020-08-29T09:06:32Z")

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Trying to get my head around AD in Julia and being inspired by Jarret Revels’ example of computing the Jacobian of a cumprod() function with ForwardDiff.jl, I tried to see whether I could get the same done with Zygote.…

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## [Creating an array of equations in ModelingToolkit](https://discourse.julialang.org/t/creating-an-array-of-equations-in-modelingtoolkit/45712)

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**Author:** [@zdenek\_hurak](https://discourse.julialang.org/u/zdenek_hurak)\
**Replies:** 2\
**Last updated:** [August 29, 2020, 2:53am UTC](https://discourse.julialang.org/t/creating-an-array-of-equations-in-modelingtoolkit/45712 "2020-08-29T02:53:04Z")

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I am trying to model a set of differential equations in ModelingToolkit. And I want to formulate it using vector variables. Namely, I will have a variable vector z = \[z₁, z₂, z₃\] (just a minimal example): julia\> using M…

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## [Symmetrical log plot](https://discourse.julialang.org/t/symmetrical-log-plot/45709)

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**Author:** [@gideonsimpson](https://discourse.julialang.org/u/gideonsimpson)\
**Replies:** 1\
**Last updated:** [August 29, 2020, 2:22am UTC](https://discourse.julialang.org/t/symmetrical-log-plot/45709 "2020-08-29T02:22:33Z")

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Is there anyway to do a symmetrical log plot (i.e., in both positive and negative directions), through Plots.jl? I know matplotlib has this functionality.

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## [Why applying an integration algorithm to whole DAEs?](https://discourse.julialang.org/t/why-applying-an-integration-algorithm-to-whole-daes/45620)

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**Author:** [@takunoda](https://discourse.julialang.org/u/takunoda)\
**Replies:** 3\
**Last updated:** [August 28, 2020, 7:04pm UTC](https://discourse.julialang.org/t/why-applying-an-integration-algorithm-to-whole-daes/45620 "2020-08-28T19:04:32Z")

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Let me ask a fundamental question which may be trivial to experts in this field. Compared with solving a set of ODEs, solving a set of DAEs is much more difficult. For instance, in the case of electrical circuits, the e…

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## [Call a PowerModels' function in Matlab](https://discourse.julialang.org/t/call-a-powermodels-function-in-matlab/45647)

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**Author:** [@Rasoul](https://discourse.julialang.org/u/Rasoul)\
**Replies:** 2\
**Last updated:** [August 28, 2020, 4:37pm UTC](https://discourse.julialang.org/t/call-a-powermodels-function-in-matlab/45647 "2020-08-28T16:37:11Z")

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Hi All, I want to call the bound tightening code in the PowerModels (i.e. following function) in Matlab. run\_obbt\_opf(case, upper\_bound, solver, model\_constructor= QCWRTriPowerModel) I tried to call “bound\_tightening\_…

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## [Setting really small values in ODE to zero](https://discourse.julialang.org/t/setting-really-small-values-in-ode-to-zero/45693)

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**Author:** [@levasco](https://discourse.julialang.org/u/levasco)\
**Replies:** 3\
**Last updated:** [August 28, 2020, 2:31pm UTC](https://discourse.julialang.org/t/setting-really-small-values-in-ode-to-zero/45693 "2020-08-28T14:31:03Z")

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In modelling biological communities with ODEs, given that individuals are somewhat finite entities, I am trying to avoid infinitesimal densities which are mathematically correct but make no sense. More specifically, I wa…

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## [Need someone to explain to me this](https://discourse.julialang.org/t/need-someone-to-explain-to-me-this/45645)

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**Author:** [@sogrbilja](https://discourse.julialang.org/u/sogrbilja)\
**Replies:** 4\
**Last updated:** [August 28, 2020, 1:24pm UTC](https://discourse.julialang.org/t/need-someone-to-explain-to-me-this/45645 "2020-08-28T13:24:13Z")

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I am very new to Julia and will learn, but I would ask you if you can help an explain this line by line to me: @constraints(model, begin # Constraint 1 - Only one value appears in each cell cell\[i in…

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## [JuliaCon 2020 Birds of a Feather](https://discourse.julialang.org/t/juliacon-2020-birds-of-a-feather/39181)

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**Author:** [@cscherrer](https://discourse.julialang.org/u/cscherrer)\
**Replies:** 24\
**Last updated:** [August 28, 2020, 12:31pm UTC](https://discourse.julialang.org/t/juliacon-2020-birds-of-a-feather/39181 "2020-08-28T12:31:48Z")

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The “Probabilistic Programming in Julia” BoF proposal was accepted! Here’s the text: Julia’s PPL community is strong and growing. The various groups already have a strong professional relationship, but a BoF would help…

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## [Always encounter this error after installing new packages on HPC?](https://discourse.julialang.org/t/always-encounter-this-error-after-installing-new-packages-on-hpc/44093)

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**Author:** [@zxjroger](https://discourse.julialang.org/u/zxjroger)\
**Replies:** 2\
**Last updated:** [August 28, 2020, 11:45am UTC](https://discourse.julialang.org/t/always-encounter-this-error-after-installing-new-packages-on-hpc/44093 "2020-08-28T11:45:24Z")

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Each time after I add a new Julia package on HPC, if I do not remove all the compiled packages in the folder “.julia/compiled” and then recompile, I will run into some random bugs. This is really annoying and I wonder wh…

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## [\[ANN\] EarthOrientation.jl](https://discourse.julialang.org/t/ann-earthorientation-jl/5200)

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**Author:** [@helgee](https://discourse.julialang.org/u/helgee)\
**Replies:** 8\
**Last updated:** [August 28, 2020, 6:39am UTC](https://discourse.julialang.org/t/ann-earthorientation-jl/5200 "2020-08-28T06:39:25Z")

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I proudly present EarthOrientation.jl. Fetch the latest IERS tables: using EarthOrientation EarthOrientation.update() Get the current Earth orientation parameters, e.g. for polar motion: xp, yp = polarmotion(now()) #…

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## [Common API for tabular data backends](https://discourse.julialang.org/t/common-api-for-tabular-data-backends/21546)

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**Author:** [@bkamins](https://discourse.julialang.org/u/bkamins)\
**Replies:** 44\
**Last updated:** [August 28, 2020, 1:35am UTC](https://discourse.julialang.org/t/common-api-for-tabular-data-backends/21546 "2020-08-28T01:35:43Z")

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Following the discussion on Slack I would like to open a topic here to discuss the possibility to provide a common API for different packages/ecosystems providing tabular data handling. The major rationale is that this …

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