# Specific Domains

**URL:** https://discourse.julialang.org/c/domain/10.md?no_subcategories=false&page=233

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**Page:** 234

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## [Trajectory DynamicalSystems.jl, DifferentialEquations.jl](https://discourse.julialang.org/t/trajectory-dynamicalsystems-jl-differentialequations-jl/90659)

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**Author:** [@Sergey\_Novak](https://discourse.julialang.org/u/Sergey_Novak)\
**Replies:** 1\
**Last updated:** [November 22, 2022, 5:26pm UTC](https://discourse.julialang.org/t/trajectory-dynamicalsystems-jl-differentialequations-jl/90659 "2022-11-22T17:26:09Z")

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Hello, i calculate trajectory of system by ODEProblem and solve from DifferentialEquations.jl and trajectory from DynamicalSystems.jl. With the same integrator parameters, they have different results, why is this? U(y) …

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## [JuMP constraint building with dot call: how to use @dot](https://discourse.julialang.org/t/jump-constraint-building-with-dot-call-how-to-use-dot/90632)

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**Author:** [@Shuhua](https://discourse.julialang.org/u/Shuhua)\
**Replies:** 1\
**Last updated:** [November 22, 2022, 4:35pm UTC](https://discourse.julialang.org/t/jump-constraint-building-with-dot-call-how-to-use-dot/90632 "2022-11-22T16:35:27Z")

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julia\> using JuMP julia\> model = JuMP.Model() julia\> @variable(model, x\[1:3\]) julia\> @variable(model, y\[1:3\]) julia\> @. @constraint(model, x \<= y) gives error: ERROR: At REPL\[19\]:1: @constraint(model, (\<=).(x, y)): …

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## [Extracting the last dt used by solver in DifferentialEquations.jl](https://discourse.julialang.org/t/extracting-the-last-dt-used-by-solver-in-differentialequations-jl/90647)

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**Author:** [@churli](https://discourse.julialang.org/u/churli)\
**Replies:** 3\
**Last updated:** [November 22, 2022, 3:13pm UTC](https://discourse.julialang.org/t/extracting-the-last-dt-used-by-solver-in-differentialequations-jl/90647 "2022-11-22T15:13:22Z")

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As per the title, I need to be able to extract the last dt used by the ODE solver from DifferentialEquations.jl . Since in my specific use case I need to extract it whenever I terminate the solver from a callback, it do…

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## [Speed up Ipopt solver](https://discourse.julialang.org/t/speed-up-ipopt-solver/89984)

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**Author:** [@Katti](https://discourse.julialang.org/u/Katti)\
**Replies:** 12\
**Last updated:** [November 22, 2022, 10:32am UTC](https://discourse.julialang.org/t/speed-up-ipopt-solver/89984 "2022-11-22T10:32:55Z")

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Hello, I have a non-linear problem which I am solving with Ipopt and JuMP. The problem originally spans over around 70 days (divided in quarter-hourly periods), but I have started to solve the model for less periods. Th…

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## [Loss functions that involve gradients](https://discourse.julialang.org/t/loss-functions-that-involve-gradients/55293)

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**Author:** [@balaji1975](https://discourse.julialang.org/u/balaji1975)\
**Replies:** 4\
**Last updated:** [November 22, 2022, 2:08am UTC](https://discourse.julialang.org/t/loss-functions-that-involve-gradients/55293 "2022-11-22T02:08:03Z")

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This is similar to this question. I am training a neural net NN(), where the loss function involves gradient of NN(.) wrt to the input. For example: m = Flux.Chain(Dense(5,5,relu), Dense(5,5,relu), Dense(5,1)) g(z) = o…

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## [Gurobi solution quality attributes prints "nothing"](https://discourse.julialang.org/t/gurobi-solution-quality-attributes-prints-nothing/90612)

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**Author:** [@MirelEce](https://discourse.julialang.org/u/MirelEce)\
**Replies:** 2\
**Last updated:** [November 22, 2022, 1:20am UTC](https://discourse.julialang.org/t/gurobi-solution-quality-attributes-prints-nothing/90612 "2022-11-22T01:20:38Z")

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Hi all! I am trying to solve a nonconvex feasibility problem with 1 quadratic constraint in Gurobi and when the model is infeasible, it doesn’t say it is infeasible and instead, it says the solution is optimal but with …

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## [Save Model Outputs](https://discourse.julialang.org/t/save-model-outputs/90465)

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**Author:** [@Yuri\_Masakazu\_Mizusa](https://discourse.julialang.org/u/Yuri_Masakazu_Mizusa)\
**Replies:** 2\
**Last updated:** [November 21, 2022, 11:27pm UTC](https://discourse.julialang.org/t/save-model-outputs/90465 "2022-11-21T23:27:49Z")

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Hi, I am running a small model several times (1000 to be more precise) and for each run I need to store the results. Usually I turn it to a DataFrame and save as a csv. But in this case I do not want to save 1000 csvs. …

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## [How to add constant value to a simple MPC Problem](https://discourse.julialang.org/t/how-to-add-constant-value-to-a-simple-mpc-problem/90575)

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**Author:** [@elliot000319](https://discourse.julialang.org/u/elliot000319)\
**Replies:** 3\
**Last updated:** [November 21, 2022, 6:09pm UTC](https://discourse.julialang.org/t/how-to-add-constant-value-to-a-simple-mpc-problem/90575 "2022-11-21T18:09:21Z")

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The following is a code that takes the current position & velocity of a box and returns the optimized trajectory of position, velocity, and acceleration. The box is placed in a 2D frictionless map. I want to add a gravit…

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## [Labels for levels in contour plot (Plots.jl)](https://discourse.julialang.org/t/labels-for-levels-in-contour-plot-plots-jl/8266)

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**Author:** [@Tamas\_Papp](https://discourse.julialang.org/u/Tamas_Papp)\
**Replies:** 10\
**Last updated:** [November 21, 2022, 5:49pm UTC](https://discourse.julialang.org/t/labels-for-levels-in-contour-plot-plots-jl/8266 "2022-11-21T17:49:42Z")

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I would like to add custom labels to a contour plot, replacing the levels. Is this possible? MWE: using Plots; pyplot() # other backend OK if necessary using StatsBase using Distributions using StatsFuns N = 100000 z =…

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## [Opposite of StatsBase.percentile](https://discourse.julialang.org/t/opposite-of-statsbase-percentile/90592)

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**Author:** [@Piotr](https://discourse.julialang.org/u/Piotr)\
**Replies:** 5\
**Last updated:** [November 21, 2022, 2:59pm UTC](https://discourse.julialang.org/t/opposite-of-statsbase-percentile/90592 "2022-11-21T14:59:43Z")

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This function returns a NUMBER for a given PERCENTILE. I don’t know what the OP had in mind, but e.g. what I am looking for right now is exactly the thing that the name of this thread points to and which is the very opp…

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## [How to make stack graph become side by side with this dataset in julia language?](https://discourse.julialang.org/t/how-to-make-stack-graph-become-side-by-side-with-this-dataset-in-julia-language/90586)

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**Author:** [@akshdfyehd](https://discourse.julialang.org/u/akshdfyehd)\
**Replies:** 0\
**Last updated:** [November 21, 2022, 1:01pm UTC](https://discourse.julialang.org/t/how-to-make-stack-graph-become-side-by-side-with-this-dataset-in-julia-language/90586 "2022-11-21T13:01:23Z")

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I have got this dataset in julia: import Downloads using DLMReader, VegaLite, InMemoryDatasets data=Downloads.download("https://raw.githubusercontent.com/akshdfyehd/salary/main/ds\_salaries.csv") ds=filereader(data,em…

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## [A headless non-interactive JSServe and WGLMakie server?](https://discourse.julialang.org/t/a-headless-non-interactive-jsserve-and-wglmakie-server/90549)

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**Author:** [@Krastanov](https://discourse.julialang.org/u/Krastanov)\
**Replies:** 2\
**Last updated:** [November 21, 2022, 2:18pm UTC](https://discourse.julialang.org/t/a-headless-non-interactive-jsserve-and-wglmakie-server/90549 "2022-11-21T14:18:51Z")

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I have a JSServe+WGLMakie visualization that works wonderfully when launched from the REPL. It is basically little more than: app = App do() dom = md"test" # and some plots that I deleted return JSServe.DOM.div(…

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## [Update text value when changing an Observable in GLMakie](https://discourse.julialang.org/t/update-text-value-when-changing-an-observable-in-glmakie/90572)

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**Author:** [@garrek](https://discourse.julialang.org/u/garrek)\
**Replies:** 4\
**Last updated:** [November 21, 2022, 12:07pm UTC](https://discourse.julialang.org/t/update-text-value-when-changing-an-observable-in-glmakie/90572 "2022-11-21T12:07:44Z")

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I’m trying to update a text value to reflect a change in one or more Observable. I’ve tried to do this a couple of ways. If the Observable is obs = Observable(1.0) I’ve tried putting it in a Label Label(fig, "$(obs)"…

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## [Zombies in biological ODE : why is my solver not sticking to zero?](https://discourse.julialang.org/t/zombies-in-biological-ode-why-is-my-solver-not-sticking-to-zero/90409)

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**Author:** [@iago-lito](https://discourse.julialang.org/u/iago-lito)\
**Replies:** 25\
**Last updated:** [November 21, 2022, 9:00am UTC](https://discourse.julialang.org/t/zombies-in-biological-ode-why-is-my-solver-not-sticking-to-zero/90409 "2022-11-21T09:00:32Z")

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Hi numerical ODE solvers enthusiasts, we’ve got a problem here that we think necessitates your kind input :slight\_smile: Here are two related questions: The following ODE system represents biological species biomasses B…

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## [Question about LP format file generation](https://discourse.julialang.org/t/question-about-lp-format-file-generation/90460)

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**Author:** [@kevinqiao](https://discourse.julialang.org/u/kevinqiao)\
**Replies:** 5\
**Last updated:** [November 21, 2022, 7:14am UTC](https://discourse.julialang.org/t/question-about-lp-format-file-generation/90460 "2022-11-21T07:14:32Z")

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I’m using JuMP v1.4.0 and I want to generate an LP format file of the following model, but it doesn’t work, the file is not generated, and I don’t know why. Thanks in advance. using JuMP using Gurobi model = Model(Gur…

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## [MLJ Tuning, MLJ](https://discourse.julialang.org/t/mlj-tuning-mlj/90544)

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**Author:** [@Mr.Benz](https://discourse.julialang.org/u/Mr.Benz)\
**Replies:** 0\
**Last updated:** [November 20, 2022, 4:06pm UTC](https://discourse.julialang.org/t/mlj-tuning-mlj/90544 "2022-11-20T16:06:14Z")

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I started with julia , new to data science. i have a quetion on MLJ tuning ang iteratied model. in a loop , Do we need to do TunedModel + IteratedModel +evaluate or IteratedModel +TunedModel +evaluate which is best…

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## [Solve a cubic equation in one variable](https://discourse.julialang.org/t/solve-a-cubic-equation-in-one-variable/90559)

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**Author:** [@GottDengDirk](https://discourse.julialang.org/u/GottDengDirk)\
**Replies:** 2\
**Last updated:** [November 20, 2022, 10:51pm UTC](https://discourse.julialang.org/t/solve-a-cubic-equation-in-one-variable/90559 "2022-11-20T22:51:49Z")

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Hi, i use PolynomialRoots.jl package. the result is but when i use Cubic Equation Calculator, there is a different result: Am I using the roots function wrong and getting different results?

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## [Creating a new column containing DataFrames itself (e.g. from "complex" function output)](https://discourse.julialang.org/t/creating-a-new-column-containing-dataframes-itself-e-g-from-complex-function-output/90550)

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**Author:** [@mreichMPI-BGC](https://discourse.julialang.org/u/mreichMPI-BGC)\
**Replies:** 2\
**Last updated:** [November 20, 2022, 7:12pm UTC](https://discourse.julialang.org/t/creating-a-new-column-containing-dataframes-itself-e-g-from-complex-function-output/90550 "2022-11-20T19:12:02Z")

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I am not sure how to best deal with function output that is not a simple scalar, when e.g. working with combine, e.g. the follow example to Calculate deciles for each numeric variable and each group: ## Create Dataset t…

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## [Summarize all or selected columns in grouped DataFrame](https://discourse.julialang.org/t/summarize-all-or-selected-columns-in-grouped-dataframe/90509)

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**Author:** [@mreichMPI-BGC](https://discourse.julialang.org/u/mreichMPI-BGC)\
**Replies:** 8\
**Last updated:** [November 20, 2022, 6:56pm UTC](https://discourse.julialang.org/t/summarize-all-or-selected-columns-in-grouped-dataframe/90509 "2022-11-20T18:56:20Z")

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Dear community, how can I summarize all columns of a GroupedDataFrame with DataFramesMeta? Like this in DataFrames: df = DataFrame(rand(20,5), :auto) df\[!, :gr\] = repeat(1:4; inner=5) dsum=combine(groupby(df, :gr), n…

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## [\[ANN\] Implementation of the subspace iteration method for the generalized EP](https://discourse.julialang.org/t/ann-implementation-of-the-subspace-iteration-method-for-the-generalized-ep/90553)

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**Author:** [@PetrKryslUCSD](https://discourse.julialang.org/u/PetrKryslUCSD)\
**Replies:** 0\
**Last updated:** [November 20, 2022, 6:53pm UTC](https://discourse.julialang.org/t/ann-implementation-of-the-subspace-iteration-method-for-the-generalized-ep/90553 "2022-11-20T18:53:37Z")

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Interested in finding the smallest eigenvalue of the generalized EP? This package might be an alternative to Arpack. It isn’t as fast, but only a little bit slower. It is all Julia, as opposed to Arpack. If you have any…

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## [JuMP set start values in new model with solution of smaller model](https://discourse.julialang.org/t/jump-set-start-values-in-new-model-with-solution-of-smaller-model/90482)

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**Author:** [@nlaws](https://discourse.julialang.org/u/nlaws)\
**Replies:** 1\
**Last updated:** [November 20, 2022, 6:20pm UTC](https://discourse.julialang.org/t/jump-set-start-values-in-new-model-with-solution-of-smaller-model/90482 "2022-11-20T18:20:20Z")

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In the JuMP docs it shows how to efficiently set start values using one model: x = all\_variables(model) x\_solution = value.(x) set\_start\_value.(x, x\_solution) However, I am looking for an efficient way to do this with …

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## [Trend Following strategy with ETFs in Julia](https://discourse.julialang.org/t/trend-following-strategy-with-etfs-in-julia/90534)

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**Author:** [@dm13450](https://discourse.julialang.org/u/dm13450)\
**Replies:** 2\
**Last updated:** [November 20, 2022, 1:09pm UTC](https://discourse.julialang.org/t/trend-following-strategy-with-etfs-in-julia/90534 "2022-11-20T13:09:59Z")

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I’ve written a post on building out a Trend Following strategy using ETFs:

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## [Can I reconstruct a network using Flux.params in Flux.jl?](https://discourse.julialang.org/t/can-i-reconstruct-a-network-using-flux-params-in-flux-jl/90531)

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**Author:** [@iHany](https://discourse.julialang.org/u/iHany)\
**Replies:** 2\
**Last updated:** [November 20, 2022, 9:31am UTC](https://discourse.julialang.org/t/can-i-reconstruct-a-network-using-flux-params-in-flux-jl/90531 "2022-11-20T09:31:04Z")

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Hi, I have a custom network nn. I can get the parameters p of nn by p = Flux.params(nn). Now, I’d like to reconstruct a neural network from the parameters. Is there any some ways to do the following? nn = NN() # con…

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## [Renaming multiple columns in Julia DataFrames](https://discourse.julialang.org/t/renaming-multiple-columns-in-julia-dataframes/83072)

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**Author:** [@mbah](https://discourse.julialang.org/u/mbah)\
**Replies:** 7\
**Last updated:** [November 20, 2022, 5:40am UTC](https://discourse.julialang.org/t/renaming-multiple-columns-in-julia-dataframes/83072 "2022-11-20T05:40:35Z")

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I have the following Julia Dataframe; data\_test = DataFrame(Time = 1:2, X1 = \[0,1\], X2 = \[10,5\]) And I have a list of names as follows; technology = \["oil", "gas"\] How do I rename columns X1 and X2 using the list (ex…

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## [Recommendations for learning basic probabilistic simulation](https://discourse.julialang.org/t/recommendations-for-learning-basic-probabilistic-simulation/90508)

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**Author:** [@samerb](https://discourse.julialang.org/u/samerb)\
**Replies:** 3\
**Last updated:** [November 19, 2022, 11:16pm UTC](https://discourse.julialang.org/t/recommendations-for-learning-basic-probabilistic-simulation/90508 "2022-11-19T23:16:59Z")

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I’m looking to learn how to do probabilistic simulations: both the math and the programming. Is there a good online course or tutorial for this in Julia (if not, just a good one for the math)? Background: I have a rudi…

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## [DynamicalSystems.jl: how to change the value of a parameter after a certain period](https://discourse.julialang.org/t/dynamicalsystems-jl-how-to-change-the-value-of-a-parameter-after-a-certain-period/88248)

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**Author:** [@josec](https://discourse.julialang.org/u/josec)\
**Replies:** 9\
**Last updated:** [November 19, 2022, 9:56pm UTC](https://discourse.julialang.org/t/dynamicalsystems-jl-how-to-change-the-value-of-a-parameter-after-a-certain-period/88248 "2022-11-19T21:56:26Z")

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Hi. I hope this question is placed in the proper category. I have studied the DynamicalSystems.jl guidelines also followed in a very useful video by Datseris (https://www.youtube.com/watch?v=13hqE\_1a158). Suppose I ha…

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## [Passing in a matrix as initial conditions versus ensemble parallel simulation in DifferentialEquations](https://discourse.julialang.org/t/passing-in-a-matrix-as-initial-conditions-versus-ensemble-parallel-simulation-in-differentialequations/90484)

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**Author:** [@kcqpo](https://discourse.julialang.org/u/kcqpo)\
**Replies:** 1\
**Last updated:** [November 19, 2022, 7:15pm UTC](https://discourse.julialang.org/t/passing-in-a-matrix-as-initial-conditions-versus-ensemble-parallel-simulation-in-differentialequations/90484 "2022-11-19T19:15:09Z")

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What’s the difference between passing in a matrix of NxM (N is the number of states, and M is the number of conditions) initial conditions and using the ensemble method?

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## [What is the difference between \`:\` and \`!\` indexing in DataFrames with Unitful?](https://discourse.julialang.org/t/what-is-the-difference-between-and-indexing-in-dataframes-with-unitful/90498)

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**Author:** [@bertulli](https://discourse.julialang.org/u/bertulli)\
**Replies:** 5\
**Last updated:** [November 19, 2022, 6:37pm UTC](https://discourse.julialang.org/t/what-is-the-difference-between-and-indexing-in-dataframes-with-unitful/90498 "2022-11-19T18:37:50Z")

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Hi all! I wanted to decorate some data I have in a DataFrame with a unit of measure from Unitful. See: julia\> df\_results\_master = DataFrame(CSV.File(f)) 468×3 DataFrame Row │ Instruction Base power mean (W) Ba…

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## [Unable to use Types from Graphs.jl and GridGraphs.jl in Jupyter Notebook](https://discourse.julialang.org/t/unable-to-use-types-from-graphs-jl-and-gridgraphs-jl-in-jupyter-notebook/88913)

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**Author:** [@MarawanEmara](https://discourse.julialang.org/u/MarawanEmara)\
**Replies:** 12\
**Last updated:** [November 19, 2022, 5:47pm UTC](https://discourse.julialang.org/t/unable-to-use-types-from-graphs-jl-and-gridgraphs-jl-in-jupyter-notebook/88913 "2022-11-19T17:47:03Z")

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Hello. I am pretty new to Julia and attempting to replicate a tutorial for InferOpt.jl (Tutorial in question is linked here: Tutorial · InferOpt.jl). I have already installed the appropriate packages for using Julia in…

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## [How to trigger non-blocking long calculations in Makie?](https://discourse.julialang.org/t/how-to-trigger-non-blocking-long-calculations-in-makie/90496)

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**Author:** [@Krastanov](https://discourse.julialang.org/u/Krastanov)\
**Replies:** 2\
**Last updated:** [November 19, 2022, 1:48pm UTC](https://discourse.julialang.org/t/how-to-trigger-non-blocking-long-calculations-in-makie/90496 "2022-11-19T13:48:16Z")

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I want to do the following in Makie: press a button which triggers long computation that interactively updates the plot. I can’t seem to figure it out. Here is a MWE: This example uses the bool observable running to tra…

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