# Specific Domains

**URL:** https://discourse.julialang.org/c/domain/10.md?no_subcategories=false&page=453

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**Page:** 454

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## [Extracting derivatives (du/dt) from an ODE problem](https://discourse.julialang.org/t/extracting-derivatives-du-dt-from-an-ode-problem/26514)

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**Author:** [@Hossein\_Haghi](https://discourse.julialang.org/u/Hossein_Haghi)\
**Replies:** 24\
**Last updated:** [April 6, 2020, 11:28pm UTC](https://discourse.julialang.org/t/extracting-derivatives-du-dt-from-an-ode-problem/26514 "2020-04-06T23:28:28Z")

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I have multiple ODE problems that I am solving. where I need the solutions (u) and derivative of the solutions (du). For smaller ODEs it is practical for me to do the following using DifferentialEquations function SB(d…

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## [LightGraphs basic usage](https://discourse.julialang.org/t/lightgraphs-basic-usage/37088)

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**Author:** [@Adriel](https://discourse.julialang.org/u/Adriel)\
**Replies:** 1\
**Last updated:** [April 6, 2020, 10:34pm UTC](https://discourse.julialang.org/t/lightgraphs-basic-usage/37088 "2020-04-06T22:34:08Z")

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Noob question. How do I add a vertex to a graph and get its value, as in the following code fragment? add\_vertex!(g) v = maximum(vertices(g)) # better way to do this? add\_edge!(g, cur, v) cur = v That works for simple …

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## [floor(BigFloat(27)^(1/3)) = 2.0; Bug in BigFloat?](https://discourse.julialang.org/t/floor-bigfloat-27-1-3-2-0-bug-in-bigfloat/37123)

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**Author:** [@Syam](https://discourse.julialang.org/u/Syam)\
**Replies:** 4\
**Last updated:** [April 6, 2020, 8:42pm UTC](https://discourse.julialang.org/t/floor-bigfloat-27-1-3-2-0-bug-in-bigfloat/37123 "2020-04-06T20:42:49Z")

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I encountered a bug in my code while using floor. With further debugging, I realized that the issue is with BigFloat. See below. julia\> floor(BigFloat(27)^(1/3)) 2.0 julia\> floor(Float64(27)^(1/3)) 3.0 julia\> ceil(Big…

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## [What is the status of the Plots ecosystem and what package should I use?](https://discourse.julialang.org/t/what-is-the-status-of-the-plots-ecosystem-and-what-package-should-i-use/18043)

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**Author:** [@affans](https://discourse.julialang.org/u/affans)\
**Replies:** 11\
**Last updated:** [April 6, 2020, 5:04pm UTC](https://discourse.julialang.org/t/what-is-the-status-of-the-plots-ecosystem-and-what-package-should-i-use/18043 "2020-04-06T17:04:01Z")

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I am coming from a ggplot2 background and would like to completely switch my workflow to Julia. What is the status of plotting in Julia? Is gadfly still viable, is vegalite hooked in with Plots.jl yet?

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## [Question about computing the partial derivatives of a multivariate polynomial](https://discourse.julialang.org/t/question-about-computing-the-partial-derivatives-of-a-multivariate-polynomial/36835)

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**Author:** [@Yusen\_Liu](https://discourse.julialang.org/u/Yusen_Liu)\
**Replies:** 5\
**Last updated:** [April 6, 2020, 8:03am UTC](https://discourse.julialang.org/t/question-about-computing-the-partial-derivatives-of-a-multivariate-polynomial/36835 "2020-04-06T08:03:03Z")

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Hi all, I got stuck on computing the partial derivatives of a multivariate polynomial. The following is my code: using TypedPolynomials using LinearAlgebra @polyvar p1 p2 p3 p4 p5 p6 p11 p12 p13 p21 p22 p23 p31 p32 p3…

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## [Interpolations: boundary conditions for the second and first derivative](https://discourse.julialang.org/t/interpolations-boundary-conditions-for-the-second-and-first-derivative/37036)

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**Author:** [@roi.holtzman](https://discourse.julialang.org/u/roi.holtzman)\
**Replies:** 4\
**Last updated:** [April 6, 2020, 10:19am UTC](https://discourse.julialang.org/t/interpolations-boundary-conditions-for-the-second-and-first-derivative/37036 "2020-04-06T10:19:53Z")

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Is there a way to have a cubic interpolation with boundary conditions for the 2nd and 1st derivative? I am using Interpolations.jl Here is an example using Interpolations, Plots x = 1:10 y = rand(10) y\[1\] = 0 y\[10\] = …

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## [Solving an optimal control problem with JuMP](https://discourse.julialang.org/t/solving-an-optimal-control-problem-with-jump/36570)

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**Author:** [@roi.holtzman](https://discourse.julialang.org/u/roi.holtzman)\
**Replies:** 16\
**Last updated:** [March 28, 2020, 4:50pm UTC](https://discourse.julialang.org/t/solving-an-optimal-control-problem-with-jump/36570 "2020-03-28T16:50:55Z")

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I am trying to solve an optimal control problem using JuMP. My problem involves a set of ODEs and an objective function that needs the final conditions of the solution of the ODEs. The input on which I want to optimize …

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## [Question about computing the determinant of matrix of indeterminate variables](https://discourse.julialang.org/t/question-about-computing-the-determinant-of-matrix-of-indeterminate-variables/36818)

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**Author:** [@Yusen\_Liu](https://discourse.julialang.org/u/Yusen_Liu)\
**Replies:** 4\
**Last updated:** [April 6, 2020, 7:01am UTC](https://discourse.julialang.org/t/question-about-computing-the-determinant-of-matrix-of-indeterminate-variables/36818 "2020-04-06T07:01:45Z")

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Hi all, I’ve been struggling with computing the determinant of the matrix of indeterminate variables. My code is as follows: using TypedPolynomials using LinearAlgebra @polyvar p1 p2 p3 p4 p5 p6 A = \[p1 p2 p3\] AT=t…

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## [How do I plot a curve in plots?](https://discourse.julialang.org/t/how-do-i-plot-a-curve-in-plots/36995)

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**Author:** [@brett\_knoss](https://discourse.julialang.org/u/brett_knoss)\
**Replies:** 23\
**Last updated:** [April 6, 2020, 1:18am UTC](https://discourse.julialang.org/t/how-do-i-plot-a-curve-in-plots/36995 "2020-04-06T01:18:12Z")

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function Π(E,W) E = 1:10 W = 1:10 sqrt(E)+4\*W end When I try to enter this function, it gives me Π as an output, and If if I try to use Π as a function, I’m told that I don’t get a function.

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## [@constraint macro vs autodiff vs provide gradient](https://discourse.julialang.org/t/constraint-macro-vs-autodiff-vs-provide-gradient/37073)

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**Author:** [@ramon.abritta](https://discourse.julialang.org/u/ramon.abritta)\
**Replies:** 2\
**Last updated:** [April 5, 2020, 11:56pm UTC](https://discourse.julialang.org/t/constraint-macro-vs-autodiff-vs-provide-gradient/37073 "2020-04-05T23:56:28Z")

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Hello, I have been using Julia for about 3 weeks. A lot still to learn. In my optimization problem, I need as much speed as possible (using Grey Wolf Optimizer with many NLP calls). I am aware that, as mentioned in JuM…

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## [Supressing verbosity of dual Models (JuMP, Dualization and Mosek)](https://discourse.julialang.org/t/supressing-verbosity-of-dual-models-jump-dualization-and-mosek/37065)

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**Author:** [@martincornejo](https://discourse.julialang.org/u/martincornejo)\
**Replies:** 2\
**Last updated:** [April 5, 2020, 7:25pm UTC](https://discourse.julialang.org/t/supressing-verbosity-of-dual-models-jump-dualization-and-mosek/37065 "2020-04-05T19:25:33Z")

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I have tried multiple methods to silence the verbosity of “dualized Mosek”. (Currently using JuMP v0.20.2 and Dualization v0.2.2) julia\> model = Model(with\_optimizer(() -\> Dualization.DualOptimizer(Mosek.Optimizer()))) …

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## [Yet another virus sim, but this time combing Actors.jl and agents](https://discourse.julialang.org/t/yet-another-virus-sim-but-this-time-combing-actors-jl-and-agents/37039)

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**Author:** [@richiejp](https://discourse.julialang.org/u/richiejp)\
**Replies:** 6\
**Last updated:** [April 5, 2020, 6:32pm UTC](https://discourse.julialang.org/t/yet-another-virus-sim-but-this-time-combing-actors-jl-and-agents/37039 "2020-04-05T18:32:51Z")

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I have implemented a toy agent based model using Actors.jl. Somehow I missed the existence of Agents.jl, but it is probably good to have a few different options. At any rate it is possible to implement the agent model w…

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## [Gradients of custom functions with Flux](https://discourse.julialang.org/t/gradients-of-custom-functions-with-flux/37041)

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**Author:** [@snisher](https://discourse.julialang.org/u/snisher)\
**Replies:** 2\
**Last updated:** [April 5, 2020, 4:46pm UTC](https://discourse.julialang.org/t/gradients-of-custom-functions-with-flux/37041 "2020-04-05T16:46:23Z")

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Hi, I’m trying to implement MAML, but I’m getting an error when calculating a gradient using Flux. The error occurs when trying to get the gradient of another function, inner\_loop. Some research indicates this is an out…

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## [Bug in var() when supplying means as vectors](https://discourse.julialang.org/t/bug-in-var-when-supplying-means-as-vectors/36979)

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**Author:** [@gabehassler](https://discourse.julialang.org/u/gabehassler)\
**Replies:** 4\
**Last updated:** [April 5, 2020, 4:36pm UTC](https://discourse.julialang.org/t/bug-in-var-when-supplying-means-as-vectors/36979 "2020-04-05T16:36:32Z")

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I’m trying to standardize (subtract the mean and divide by the standard deviation) of each column in a matrix. In doing so, I think I’v discovered a bug in the var() function when supplying the means. The following code…

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## [Got good results for some tasks and got an error for other tasks in a job array?](https://discourse.julialang.org/t/got-good-results-for-some-tasks-and-got-an-error-for-other-tasks-in-a-job-array/37049)

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**Author:** [@zxjroger](https://discourse.julialang.org/u/zxjroger)\
**Replies:** 2\
**Last updated:** [April 5, 2020, 4:22pm UTC](https://discourse.julialang.org/t/got-good-results-for-some-tasks-and-got-an-error-for-other-tasks-in-a-job-array/37049 "2020-04-05T16:22:42Z")

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I am using my university HPC cluster and I have a job array to do some similar optimization problems using the package Optim.jl. Tasks should use the same packages and etc. They should only differ in the starting values.…

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## [SIR modeling in Soss](https://discourse.julialang.org/t/sir-modeling-in-soss/36680)

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**Author:** [@cscherrer](https://discourse.julialang.org/u/cscherrer)\
**Replies:** 16\
**Last updated:** [April 5, 2020, 3:31pm UTC](https://discourse.julialang.org/t/sir-modeling-in-soss/36680 "2020-04-05T15:31:10Z")

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I spent some time yesterday getting as SIR epidemiology model working in Soss. I see this a lot as a differential equation, but that doesn’t make sense for real data, because what we really observe are counts. So I used …

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## ["Your CUDA installation does not provide libcudadevrt" even though it is available in /usr/local/cuda-10.0](https://discourse.julialang.org/t/your-cuda-installation-does-not-provide-libcudadevrt-even-though-it-is-available-in-usr-local-cuda-10-0/37011)

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**Author:** [@rmz](https://discourse.julialang.org/u/rmz)\
**Replies:** 4\
**Last updated:** [April 5, 2020, 10:19am UTC](https://discourse.julialang.org/t/your-cuda-installation-does-not-provide-libcudadevrt-even-though-it-is-available-in-usr-local-cuda-10-0/37011 "2020-04-05T10:19:16Z")

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I’ve gotten access to a nice machine with a rack full of GPUs running ubuntu. However I can’t get Julia 1.4.0 to use any of the GPUs. Do you have any suggestions for investegations I could do to figure out what’s wrong…

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## [Why does Pkg.update() downgrade from Flux0.10 to 0.8?](https://discourse.julialang.org/t/why-does-pkg-update-downgrade-from-flux0-10-to-0-8/37043)

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**Author:** [@jaynick](https://discourse.julialang.org/u/jaynick)\
**Replies:** 1\
**Last updated:** [April 5, 2020, 8:14am UTC](https://discourse.julialang.org/t/why-does-pkg-update-downgrade-from-flux0-10-to-0-8/37043 "2020-04-05T08:14:21Z")

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Hello I just installed julia1.4 (mac), and was installing needed packages. From previous experience, I know that the thing to do is install Flux first, then install other packages, that way it will select compatible pa…

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## [Multilple plots on the same gragh](https://discourse.julialang.org/t/multilple-plots-on-the-same-gragh/37040)

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**Author:** [@brett\_knoss](https://discourse.julialang.org/u/brett_knoss)\
**Replies:** 2\
**Last updated:** [April 5, 2020, 1:15am UTC](https://discourse.julialang.org/t/multilple-plots-on-the-same-gragh/37040 "2020-04-05T01:15:16Z")

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I’m able to graph two functions with plots using Plots U(E,W)= (40-E)^2/sqrt(W) #Utility function E = 0:40 W = 10:100 UC=contour(E,W,U) B(E,W)= -(40-E)/W # budget line function E = 0:40 BL=contour(E,W,B) How would I…

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## [Check if a solver supports VariablePrimalStart](https://discourse.julialang.org/t/check-if-a-solver-supports-variableprimalstart/37015)

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**Author:** [@ohmsweetohm1](https://discourse.julialang.org/u/ohmsweetohm1)\
**Replies:** 1\
**Last updated:** [April 4, 2020, 9:32pm UTC](https://discourse.julialang.org/t/check-if-a-solver-supports-variableprimalstart/37015 "2020-04-04T21:32:49Z")

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Is there a way to check if a solver supports MOI.VariablePrimalStart? Something like this: MOI.supports(JuMP.backend(m), MOI.VariablePrimalStart) but it seems that I’m missing something:

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## [Standardize dataset with StatsBase](https://discourse.julialang.org/t/standardize-dataset-with-statsbase/37034)

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**Author:** [@alequa](https://discourse.julialang.org/u/alequa)\
**Replies:** 1\
**Last updated:** [April 4, 2020, 8:00pm UTC](https://discourse.julialang.org/t/standardize-dataset-with-statsbase/37034 "2020-04-04T20:00:00Z")

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Hi, I am trying to apply this standardization scheme where you standardize the test set on the base of the train set. I am trying to do this with the ZScoreTransform of StatsBase, but I encounter this trouble. # usin…

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## [Flux custom layers - incorrect solution from training](https://discourse.julialang.org/t/flux-custom-layers-incorrect-solution-from-training/36993)

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**Author:** [@lwhitefox](https://discourse.julialang.org/u/lwhitefox)\
**Replies:** 0\
**Last updated:** [April 3, 2020, 11:21pm UTC](https://discourse.julialang.org/t/flux-custom-layers-incorrect-solution-from-training/36993 "2020-04-03T23:21:20Z")

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My real goal is to include layers with matrices computed from known physics solutions; the training will then determine physical parameters appearing in the equations used to compute the matrix elements. To get started,…

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## [Understand this part of the Zygote docs](https://discourse.julialang.org/t/understand-this-part-of-the-zygote-docs/36816)

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**Author:** [@jaynick](https://discourse.julialang.org/u/jaynick)\
**Replies:** 2\
**Last updated:** [April 3, 2020, 8:24pm UTC](https://discourse.julialang.org/t/understand-this-part-of-the-zygote-docs/36816 "2020-04-03T20:24:32Z")

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I am wondering if there are several typos in introduction example to custom adjoints, https://fluxml.ai/Zygote.jl/dev/adjoints/ In other words pullback(sin, x) behaves the same as dsin(x) = sin(x), ȳ -\> (ȳ \* cos(x)…

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## [Matrix formulation of multiple regression](https://discourse.julialang.org/t/matrix-formulation-of-multiple-regression/33358)

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**Author:** [@mthelm85](https://discourse.julialang.org/u/mthelm85)\
**Replies:** 3\
**Last updated:** [April 3, 2020, 4:56pm UTC](https://discourse.julialang.org/t/matrix-formulation-of-multiple-regression/33358 "2020-04-03T16:56:52Z")

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I’ve been studying linear algebra and I decided I would see what it takes to code a multiple regression model from scratch to deepen my understanding of some of the things I’ve been learning. I couldn’t really find any J…

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## [Zygote custom adjoint has surprising performance effects](https://discourse.julialang.org/t/zygote-custom-adjoint-has-surprising-performance-effects/36972)

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**Author:** [@SEA](https://discourse.julialang.org/u/SEA)\
**Replies:** 0\
**Last updated:** [April 3, 2020, 3:26pm UTC](https://discourse.julialang.org/t/zygote-custom-adjoint-has-surprising-performance-effects/36972 "2020-04-03T15:26:03Z")

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I am experimenting with custom adjoints in Zygote. In the following code, I defined an adjoint for the function gauss. Surprisingly, benchmarking gradient on gauss and a “wrapper” closure f around gauss shows that the gr…

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## [Does someone have experience in Augmented Lagrangian in julia?](https://discourse.julialang.org/t/does-someone-have-experience-in-augmented-lagrangian-in-julia/36872)

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**Author:** [@Markus\_Hauschel](https://discourse.julialang.org/u/Markus_Hauschel)\
**Replies:** 12\
**Last updated:** [April 3, 2020, 2:23pm UTC](https://discourse.julialang.org/t/does-someone-have-experience-in-augmented-lagrangian-in-julia/36872 "2020-04-03T14:23:10Z")

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It seems that most of the posts, I can find, are old. My code is currently in R and I think about porting to Julia. Does it work well?

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## [COVID-19 - Model and ODE delay equations](https://discourse.julialang.org/t/covid-19-model-and-ode-delay-equations/36632)

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**Author:** [@Emmanuel-R8](https://discourse.julialang.org/u/Emmanuel-R8)\
**Replies:** 19\
**Last updated:** [April 3, 2020, 1:53pm UTC](https://discourse.julialang.org/t/covid-19-model-and-ode-delay-equations/36632 "2020-04-03T13:53:38Z")

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I have a working model and parameter optimiser for the COVID-19 epidemy (Emmanuel-R8/COVID-19-Julia\](\[GitHub - Emmanuel-R8/COVID-19-Julia: A re-implementation of the Neherlab.org model in Julia). The model is inspired (b…

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## [Multiple Computer Example](https://discourse.julialang.org/t/multiple-computer-example/10518)

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**Author:** [@iwelch](https://discourse.julialang.org/u/iwelch)\
**Replies:** 11\
**Last updated:** [April 3, 2020, 11:07am UTC](https://discourse.julialang.org/t/multiple-computer-example/10518 "2020-04-03T11:07:23Z")

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Does anybody have a really simple example of a local host farming out a task to another ssh-connected computer (with julia on it)? think @everywhere function abc(n::Int) sum=0; for i=1:n; sum+=i; end;#for r…

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## [Simple SEIR model for simulating Covid-19 outbreak](https://discourse.julialang.org/t/simple-seir-model-for-simulating-covid-19-outbreak/35854)

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**Author:** [@Bernd\_Blasius](https://discourse.julialang.org/u/Bernd_Blasius)\
**Replies:** 1\
**Last updated:** [April 3, 2020, 9:07am UTC](https://discourse.julialang.org/t/simple-seir-model-for-simulating-covid-19-outbreak/35854 "2020-04-03T09:07:12Z")

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Implementation of a SEIR-like model describing the Coronavirus Covid-19 outbreak 2019/20, based on the publication: Wang et al. (2020) Evolving epidemiology and impact of non-pharmaceutical interventions on the outbreak …

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## [How to use Julia to create Golden section search](https://discourse.julialang.org/t/how-to-use-julia-to-create-golden-section-search/36916)

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**Author:** [@11129](https://discourse.julialang.org/u/11129)\
**Replies:** 5\
**Last updated:** [April 3, 2020, 5:22am UTC](https://discourse.julialang.org/t/how-to-use-julia-to-create-golden-section-search/36916 "2020-04-03T05:22:39Z")

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How to use code to reach the Golden section search.

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