# Specific Domains

**URL:** https://discourse.julialang.org/c/domain/10.md?no_subcategories=false&page=451

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**Page:** 452

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## [Eigensolver for Complex Companion Matrix](https://discourse.julialang.org/t/eigensolver-for-complex-companion-matrix/37587)

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**Author:** [@Arrigo\_Benedetti](https://discourse.julialang.org/u/Arrigo_Benedetti)\
**Replies:** 10\
**Last updated:** [April 14, 2020, 9:22pm UTC](https://discourse.julialang.org/t/eigensolver-for-complex-companion-matrix/37587 "2020-04-14T21:22:01Z")

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I’m wondering if there is any Julia eigensolver specialized for complex companion matrices of moderate size, say up to 30x30. Thanks, -Arrigo

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## [Specific help regarding allocations and performance](https://discourse.julialang.org/t/specific-help-regarding-allocations-and-performance/37572)

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**Author:** [@Ahmed\_Salih](https://discourse.julialang.org/u/Ahmed_Salih)\
**Replies:** 15\
**Last updated:** [April 14, 2020, 8:42pm UTC](https://discourse.julialang.org/t/specific-help-regarding-allocations-and-performance/37572 "2020-04-14T20:42:20Z")

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Hello! I am working on a tool in Julia which allows one to redistribute an initial set of particles inside a profile based on SPH (smoothed particle hydrodynamics), to get a more uniform distribution. The algorithm is b…

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## [Fixing a variable](https://discourse.julialang.org/t/fixing-a-variable/37569)

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**Author:** [@Smith](https://discourse.julialang.org/u/Smith)\
**Replies:** 2\
**Last updated:** [April 14, 2020, 4:17pm UTC](https://discourse.julialang.org/t/fixing-a-variable/37569 "2020-04-14T16:17:49Z")

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Here it is mentioned fixing a variable is better than adding a constraint: Does JuMP.fix and setting bounds on variables work with vectors or loop is necessary? I have only managed it with a loop: for i = 15:25 JuMP.fi…

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## [Contour plot for 2d kernel density](https://discourse.julialang.org/t/contour-plot-for-2d-kernel-density/37223)

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**Author:** [@Tamas\_Papp](https://discourse.julialang.org/u/Tamas_Papp)\
**Replies:** 9\
**Last updated:** [April 14, 2020, 9:57am UTC](https://discourse.julialang.org/t/contour-plot-for-2d-kernel-density/37223 "2020-04-14T09:57:45Z")

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I need to visualize about 10^5 points on a 2D scatterplot, with four categories. What I am currently doing is fitting a kernel density using KernelDensity.kde, making a rectangular grid, finding the contours with Coun…

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## [Reddit discussion: limitations of Zygote](https://discourse.julialang.org/t/reddit-discussion-limitations-of-zygote/36982)

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**Author:** [@jaynick](https://discourse.julialang.org/u/jaynick)\
**Replies:** 15\
**Last updated:** [April 14, 2020, 9:12am UTC](https://discourse.julialang.org/t/reddit-discussion-limitations-of-zygote/36982 "2020-04-14T09:12:09Z")

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There is a reddit discussion of the swift/tensorflow project that has a couple comments about Julia. I am interested in this statement - to what extent is this true? If the end goal is to “differentiate all the things…

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## [Possible anonymous function bug in Flux](https://discourse.julialang.org/t/possible-anonymous-function-bug-in-flux/26389)

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**Author:** [@stu](https://discourse.julialang.org/u/stu)\
**Replies:** 9\
**Last updated:** [April 14, 2020, 5:49am UTC](https://discourse.julialang.org/t/possible-anonymous-function-bug-in-flux/26389 "2020-04-14T05:49:07Z")

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Has anyone noticed that m = Chain(Dense(5, 2), Dense(2, 2) Dense(2, 5)) produces an entirely result than m = Chain(x -\> Dense(5, 2)(x), Dense(2, 2) Dense(2, 5)) are anonymous functions somehow not supported for Chain…

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## [Generic Function to train NN w/ Flux](https://discourse.julialang.org/t/generic-function-to-train-nn-w-flux/37208)

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**Author:** [@Albert\_Zevelev](https://discourse.julialang.org/u/Albert_Zevelev)\
**Replies:** 7\
**Last updated:** [April 14, 2020, 3:47am UTC](https://discourse.julialang.org/t/generic-function-to-train-nn-w-flux/37208 "2020-04-14T03:47:30Z")

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Updated: I would like to write a generic function to train a model in Flux. An ordinary linear regression w/ intercept is a special case of a neural network. If the optimizers work well I should get the same result (es…

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## [Franklin deployment problems](https://discourse.julialang.org/t/franklin-deployment-problems/37519)

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**Author:** [@KajWiik](https://discourse.julialang.org/u/KajWiik)\
**Replies:** 11\
**Last updated:** [April 13, 2020, 9:49pm UTC](https://discourse.julialang.org/t/franklin-deployment-problems/37519 "2020-04-13T21:49:41Z")

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I have a locally working Franklin website and have difficulties in deploying it to github. I have tried both with the current documentation and https://github.com/tlienart/Franklin.jl/issues/390 The problem seems to be …

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## [Grid layout for multiple plots](https://discourse.julialang.org/t/grid-layout-for-multiple-plots/37528)

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**Author:** [@Farhan\_Samir](https://discourse.julialang.org/u/Farhan_Samir)\
**Replies:** 2\
**Last updated:** [April 13, 2020, 8:42pm UTC](https://discourse.julialang.org/t/grid-layout-for-multiple-plots/37528 "2020-04-13T20:42:54Z")

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Hi, I’m trying to create a 2 by 10 grid of plots. The Plots documentation provides an example for a 2x2 grid: plot(rand(10,4), layout=grid(2,2),ticks=nothing) However, extending this to plot(rand(10,20),layout=grid(2…

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## [Complex admittance matrix in PowerModels.jl?](https://discourse.julialang.org/t/complex-admittance-matrix-in-powermodels-jl/36717)

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**Author:** [@RibeiroRaul](https://discourse.julialang.org/u/RibeiroRaul)\
**Replies:** 2\
**Last updated:** [April 13, 2020, 2:51pm UTC](https://discourse.julialang.org/t/complex-admittance-matrix-in-powermodels-jl/36717 "2020-04-13T14:51:59Z")

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Hi, Is there a function that retrieves the complex admittance matrix from a PowerModels dict. Even though there is a type AdmittanceMatrix, it seems that it only receives susceptance matrix from calc\_susceptance\_matrix…

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## [ML for optimal power flow](https://discourse.julialang.org/t/ml-for-optimal-power-flow/37501)

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**Author:** [@Mariana](https://discourse.julialang.org/u/Mariana)\
**Replies:** 0\
**Last updated:** [April 13, 2020, 11:53am UTC](https://discourse.julialang.org/t/ml-for-optimal-power-flow/37501 "2020-04-13T11:53:24Z")

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I’d like to use neural networks to estimate some variable on an optimal power flow problem. For example, I’d like to estimate the power flow on transmission lines, given the system topology (generation, demand, line para…

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## [Genie.jl in Julia vs Plotly-express in Python](https://discourse.julialang.org/t/genie-jl-in-julia-vs-plotly-express-in-python/37447)

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**Author:** [@anon69491625](https://discourse.julialang.org/u/anon69491625)\
**Replies:** 2\
**Last updated:** [April 12, 2020, 3:31pm UTC](https://discourse.julialang.org/t/genie-jl-in-julia-vs-plotly-express-in-python/37447 "2020-04-12T15:31:01Z")

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anyone out there had a chance to code in both Genie.jl and Plotly-express ( Or Dash). I’d like to hear their opinions on comparing Genie.jl vs Plotly-express OR Dash.

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## [Tanmay Bakshi tried to teach me ML, but I failed and I don't know why](https://discourse.julialang.org/t/tanmay-bakshi-tried-to-teach-me-ml-but-i-failed-and-i-dont-know-why/37415)

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**Author:** [@Klaus](https://discourse.julialang.org/u/Klaus)\
**Replies:** 4\
**Last updated:** [April 12, 2020, 1:39pm UTC](https://discourse.julialang.org/t/tanmay-bakshi-tried-to-teach-me-ml-but-i-failed-and-i-dont-know-why/37415 "2020-04-12T13:39:08Z")

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I tried this code snippet from the book (…springboard to machine learning for all ages): using Metalhead: VGG19, preprocess, load, labels using Flux: onecold model = VGG19() class\_labels = labels(model) print("Enter t…

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## [Help with Puzzle Solver Program](https://discourse.julialang.org/t/help-with-puzzle-solver-program/37412)

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**Author:** [@peterfarrell66](https://discourse.julialang.org/u/peterfarrell66)\
**Replies:** 5\
**Last updated:** [April 12, 2020, 4:30am UTC](https://discourse.julialang.org/t/help-with-puzzle-solver-program/37412 "2020-04-12T04:30:08Z")

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Hi! I’m new to Julia but I’ve had years of experience using Python and some Javascript too. I wrote a puzzle solving program in Python and got a big speedup when I translated it to Javascript. I’ve taken a bash at a Jul…

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## [Minijyro - a toy Pyro-like PPL](https://discourse.julialang.org/t/minijyro-a-toy-pyro-like-ppl/37356)

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**Author:** [@treichelt](https://discourse.julialang.org/u/treichelt)\
**Replies:** 5\
**Last updated:** [April 12, 2020, 1:00am UTC](https://discourse.julialang.org/t/minijyro-a-toy-pyro-like-ppl/37356 "2020-04-12T01:00:56Z")

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Hi everyone, I implemented a small PPL, Minijyro.jl, that is based on the ideas of effect handlers in Pyro and thought it might be of interest to people. This project is mostly me trying to learn more about Julia and pr…

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## [Using ForwardDiff to differentiate an ODE with respect to some of its parameters](https://discourse.julialang.org/t/using-forwarddiff-to-differentiate-an-ode-with-respect-to-some-of-its-parameters/37353)

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**Author:** [@peterj](https://discourse.julialang.org/u/peterj)\
**Replies:** 5\
**Last updated:** [April 10, 2020, 6:38pm UTC](https://discourse.julialang.org/t/using-forwarddiff-to-differentiate-an-ode-with-respect-to-some-of-its-parameters/37353 "2020-04-10T18:38:35Z")

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So far, I have this using DifferentialEquations using LabelledArrays const n = 10 struct params p\_to\_optimize\_array::AbstractArray{\<:Real,1} p\_constant\_array::AbstractArray{\<:Real,1} end function f1(du,u…

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## [Gaston to plot Cobb Douglas, not sure how to set scale](https://discourse.julialang.org/t/gaston-to-plot-cobb-douglas-not-sure-how-to-set-scale/37369)

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**Author:** [@brett\_knoss](https://discourse.julialang.org/u/brett_knoss)\
**Replies:** 3\
**Last updated:** [April 11, 2020, 5:16pm UTC](https://discourse.julialang.org/t/gaston-to-plot-cobb-douglas-not-sure-how-to-set-scale/37369 "2020-04-11T17:16:41Z")

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I’m trying to model the above function L= 0:600 K=0:600 Q=0:8000 surf(L, K, (L,K)-\>.1\*K^.5\*L^1.5, title="Cobb Douglas", plotstyle="lines", linecolor="magenta", gpcom="unset colorbox") surf!(x,y,(x,y)-\>cos.(x/…

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## [Sparse Cholesky of Gram Matrix (SuiteSparse?)](https://discourse.julialang.org/t/sparse-cholesky-of-gram-matrix-suitesparse/37303)

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**Author:** [@guille](https://discourse.julialang.org/u/guille)\
**Replies:** 25\
**Last updated:** [April 11, 2020, 3:07pm UTC](https://discourse.julialang.org/t/sparse-cholesky-of-gram-matrix-suitesparse/37303 "2020-04-11T15:07:47Z")

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Hey all! I have a quick question, which I saw was referenced here some time ago. I was wondering if there was a standard way of factorizing A^TA (i.e. the Gram matrix of A) without actively computing the Gram matrix? Th…

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## [Change thickness of axises in plots](https://discourse.julialang.org/t/change-thickness-of-axises-in-plots/37387)

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**Author:** [@Torkel](https://discourse.julialang.org/u/Torkel)\
**Replies:** 0\
**Last updated:** [April 11, 2020, 11:21am UTC](https://discourse.julialang.org/t/change-thickness-of-axises-in-plots/37387 "2020-04-11T11:21:56Z")

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Hello, how do I change the thickness of the axes when I make a plot (without changes the thickness of texts, ticks, etc.)?

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## [Tangent Curves to Linear Functions (Wages and Cobb Douglas)](https://discourse.julialang.org/t/tangent-curves-to-linear-functions-wages-and-cobb-douglas/37377)

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**Author:** [@brett\_knoss](https://discourse.julialang.org/u/brett_knoss)\
**Replies:** 0\
**Last updated:** [April 11, 2020, 3:18am UTC](https://discourse.julialang.org/t/tangent-curves-to-linear-functions-wages-and-cobb-douglas/37377 "2020-04-11T03:18:53Z")

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using Gnuplot, Gaston, Convex, SCS L= 0:600 K=0:600 C=0:600 Q=0:8000 contour(K, L, (K,L)-\>.1\*K^.5\*L^1.5, xlabel="Leisure", ylabel="Consumption",labels=false) #same function as a contour graph for somereason, doesn't r…

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## [Best flux for Tracker: 0.9 or 0.8.3?](https://discourse.julialang.org/t/best-flux-for-tracker-0-9-or-0-8-3/37143)

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**Author:** [@jaynick](https://discourse.julialang.org/u/jaynick)\
**Replies:** 2\
**Last updated:** [April 11, 2020, 3:08am UTC](https://discourse.julialang.org/t/best-flux-for-tracker-0-9-or-0-8-3/37143 "2020-04-11T03:08:31Z")

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A post in this recent discussion recommends using Tracker rather than Zygote if one is less adventurous. I am undecided, but, if one is to use Tracker, which version of Flux is best?

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## [Model Predictive Control (MPC) in Julia](https://discourse.julialang.org/t/model-predictive-control-mpc-in-julia/24240)

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**Author:** [@uwechsler](https://discourse.julialang.org/u/uwechsler)\
**Replies:** 24\
**Last updated:** [April 11, 2020, 3:04am UTC](https://discourse.julialang.org/t/model-predictive-control-mpc-in-julia/24240 "2020-04-11T03:04:16Z")

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I am considering using Julia and JuMP for my Master Thesis in learning based robust economic Model Predictive Control. I hope to get some feedback from the community on what packages to use or on what functionalities are…

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## [Help for improvement for drawing shapefile using Gadfly](https://discourse.julialang.org/t/help-for-improvement-for-drawing-shapefile-using-gadfly/37348)

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**Author:** [@L\_Adam](https://discourse.julialang.org/u/L_Adam)\
**Replies:** 4\
**Last updated:** [April 11, 2020, 2:55am UTC](https://discourse.julialang.org/t/help-for-improvement-for-drawing-shapefile-using-gadfly/37348 "2020-04-11T02:55:46Z")

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I use Shapefile.jl parse \*.shp file into DataFrame, with each row having some region information and a Polygon struct specifies the shape of that region. Everything works smoothly. Big thanks :kissing\_smiling\_eyes: Afte…

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## [Calculating the analytical solution of an Ornstein-Uhlenbeck SDE](https://discourse.julialang.org/t/calculating-the-analytical-solution-of-an-ornstein-uhlenbeck-sde/37359)

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**Author:** [@williamjsdavis](https://discourse.julialang.org/u/williamjsdavis)\
**Replies:** 2\
**Last updated:** [April 10, 2020, 6:04pm UTC](https://discourse.julialang.org/t/calculating-the-analytical-solution-of-an-ornstein-uhlenbeck-sde/37359 "2020-04-10T18:04:25Z")

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I want to compare different SDE solvers against the analytical solution for the Ornstein-Uhlenbeck process. Currently I am doing this by solving numerically first (e.g. Euler-Maruyama), saving the noise, and calculating …

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## [Regridding 3d array](https://discourse.julialang.org/t/regridding-3d-array/37349)

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**Author:** [@asb](https://discourse.julialang.org/u/asb)\
**Replies:** 1\
**Last updated:** [April 10, 2020, 5:37pm UTC](https://discourse.julialang.org/t/regridding-3d-array/37349 "2020-04-10T17:37:32Z")

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nub question. I have a 3d array of input data1 of dimensions \[nx,ny,nz\] The data represent a 3D continuous function sampled on an irregular grid. data\[i,j,k\] is the data at grid point \[i,j,k\]. xgrid1\[i,j,k\] are the x…

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## [ArgumentError: cannot take the CPU address of a CuArray when using selectdim](https://discourse.julialang.org/t/argumenterror-cannot-take-the-cpu-address-of-a-cuarray-when-using-selectdim/37281)

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**Author:** [@Geoffrey](https://discourse.julialang.org/u/Geoffrey)\
**Replies:** 4\
**Last updated:** [April 10, 2020, 5:06pm UTC](https://discourse.julialang.org/t/argumenterror-cannot-take-the-cpu-address-of-a-cuarray-when-using-selectdim/37281 "2020-04-10T17:06:11Z")

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Hi, I’m quite new to Julia computing and even more to GPU computing but I notice that selectdim function from julia output is stored on the CPU acording to this error: “ERROR: ArgumentError: cannot take the CPU address …

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## [Parallel processing](https://discourse.julialang.org/t/parallel-processing/37319)

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**Author:** [@ohmsweetohm1](https://discourse.julialang.org/u/ohmsweetohm1)\
**Replies:** 7\
**Last updated:** [April 10, 2020, 3:19pm UTC](https://discourse.julialang.org/t/parallel-processing/37319 "2020-04-10T15:19:02Z")

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I did some experiments with parallel processing, i.e. solving models in parallel. But the result is not what I expected: using Distributed import JuMP addprocs(4) function simple\_model(a, b) model = JuMP.Model() …

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## [Correct formula for MixedModels, lme4](https://discourse.julialang.org/t/correct-formula-for-mixedmodels-lme4/37343)

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**Author:** [@Enrico\_Schulz](https://discourse.julialang.org/u/Enrico_Schulz)\
**Replies:** 0\
**Last updated:** [April 10, 2020, 1:59pm UTC](https://discourse.julialang.org/t/correct-formula-for-mixedmodels-lme4/37343 "2020-04-10T13:59:21Z")

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Dear statistics experts, I am using MixedModels.jl in Julia with this formula: f2 = @formula(fmri~AMP+SLP+aSLP+(0+AMP|session)+(0+SLP|session)+(0+aSLP|session)); The toolbox in Julia is from Douglas Bates und the form…

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## [Nested Multivariate Regression](https://discourse.julialang.org/t/nested-multivariate-regression/36710)

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**Author:** [@Humphrey\_Lee](https://discourse.julialang.org/u/Humphrey_Lee)\
**Replies:** 8\
**Last updated:** [April 10, 2020, 7:28am UTC](https://discourse.julialang.org/t/nested-multivariate-regression/36710 "2020-04-10T07:28:41Z")

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Title: Nested Multivariate Regression Appreciate some guidance and sample codes. I’m new to Julia language, but have used Python and R a bit. This is a curve fitting / regression of data (csv) exercise. The equation to …

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## [Array index which is an index of another array](https://discourse.julialang.org/t/array-index-which-is-an-index-of-another-array/37285)

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**Author:** [@jakub1998](https://discourse.julialang.org/u/jakub1998)\
**Replies:** 1\
**Last updated:** [April 9, 2020, 4:13pm UTC](https://discourse.julialang.org/t/array-index-which-is-an-index-of-another-array/37285 "2020-04-09T16:13:27Z")

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I have to solve a problem with permutations. The function takes vector a with n elements as a parameter. I declare b as @variable - there should be the permutation 1:n that gives the best result after finding t…

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