# Specific Domains

**URL:** https://discourse.julialang.org/c/domain/10.md?no_subcategories=false&page=440

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**Page:** 441

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## [Best Solver for Bessel-like Differential Equations with Singularity; unexpected Interpolation Behavior](https://discourse.julialang.org/t/best-solver-for-bessel-like-differential-equations-with-singularity-unexpected-interpolation-behavior/41482)

<div class="topic-metadata">

**Author:** [@CosmoProf](https://discourse.julialang.org/u/CosmoProf)\
**Replies:** 6\
**Last updated:** [June 17, 2020, 2:27am UTC](https://discourse.julialang.org/t/best-solver-for-bessel-like-differential-equations-with-singularity-unexpected-interpolation-behavior/41482 "2020-06-17T02:27:20Z")

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Hi, I’m starting a project solving equations (using the DifferentialEquations.jl package) that will be similar to Bessel equations: oscillatory in general, with a singularity in the function and its derivatives at t=0. (…

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## [Stack overflow error with @SDconstraint](https://discourse.julialang.org/t/stack-overflow-error-with-sdconstraint/41557)

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**Author:** [@stephentu](https://discourse.julialang.org/u/stephentu)\
**Replies:** 3\
**Last updated:** [June 17, 2020, 12:59am UTC](https://discourse.julialang.org/t/stack-overflow-error-with-sdconstraint/41557 "2020-06-17T00:59:30Z")

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I have the following simple code snippet which is causing me issues: function find\_common\_lyapunov(system::PiecewiseLinearSystem, gamma::Float64) @assert(gamma \> 0.0) dim = system\_dim(system) model = Model(M…

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## [Updating to MCMCChains v4.0.0 results in Turing downgrade](https://discourse.julialang.org/t/updating-to-mcmcchains-v4-0-0-results-in-turing-downgrade/41463)

<div class="topic-metadata">

**Author:** [@EricChameroy](https://discourse.julialang.org/u/EricChameroy)\
**Replies:** 9\
**Last updated:** [June 16, 2020, 7:23pm UTC](https://discourse.julialang.org/t/updating-to-mcmcchains-v4-0-0-results-in-turing-downgrade/41463 "2020-06-16T19:23:19Z")

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Upgrading to the latest MCMChains results in Turing downgrading from v0.13.0 to v0.7.1. Has anyone else had this issue? Is there a workaround? In the meantime, I’ve pinned Turing to prevent the downgrade. Should I repor…

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## [How to use the summation in Julia?](https://discourse.julialang.org/t/how-to-use-the-summation-in-julia/41522)

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**Author:** [@RaquelSantos](https://discourse.julialang.org/u/RaquelSantos)\
**Replies:** 5\
**Last updated:** [June 16, 2020, 6:07pm UTC](https://discourse.julialang.org/t/how-to-use-the-summation-in-julia/41522 "2020-06-16T18:07:52Z")

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I need to put this objective function in Julia, but I don’t know how to build a sum that has 3 indexes. Can someone help me? I started doing like this using JuMP, Cbc Model1 = Model(with\_optimizer(Cbc.Optimizer)) CR …

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## [Playing with function composition, is there a name for what I'm doing?](https://discourse.julialang.org/t/playing-with-function-composition-is-there-a-name-for-what-im-doing/41533)

<div class="topic-metadata">

**Author:** [@klaff](https://discourse.julialang.org/u/klaff)\
**Replies:** 2\
**Last updated:** [June 16, 2020, 5:06pm UTC](https://discourse.julialang.org/t/playing-with-function-composition-is-there-a-name-for-what-im-doing/41533 "2020-06-16T17:06:34Z")

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For AC analysis of circuits the following is handy: using Plots ZL(L) = f -\> im\*2π\*f\*L ZC(C) = f -\> 1/(im\*2π\*f\*C) ZR(R) = f -\> R series(a,b,c...) = f -\> sum(\[x(f) for x in \[\[a,b\]; \[c...\]\]\]) parallel(a,b,c...) = f -\> 1/…

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## [Can I draw dot lines with GraphRecipes.jl?](https://discourse.julialang.org/t/can-i-draw-dot-lines-with-graphrecipes-jl/41495)

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**Author:** [@larrylan](https://discourse.julialang.org/u/larrylan)\
**Replies:** 0\
**Last updated:** [June 16, 2020, 4:17am UTC](https://discourse.julialang.org/t/can-i-draw-dot-lines-with-graphrecipes-jl/41495 "2020-06-16T04:17:06Z")

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Greetings, I’m trying to use GraphRecipes to draw networks because I can spot nodes with their specific coordinates with GraphRecipes, e.g. this simple example GitHub - JuliaPlots/GraphRecipes.jl: Graph-related recipes …

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## [Common RL Environment Interface](https://discourse.julialang.org/t/common-rl-environment-interface/41460)

<div class="topic-metadata">

**Author:** [@zsunberg](https://discourse.julialang.org/u/zsunberg)\
**Replies:** 1\
**Last updated:** [June 15, 2020, 9:12pm UTC](https://discourse.julialang.org/t/common-rl-environment-interface/41460 "2020-06-15T21:12:55Z")

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Hi everyone, after this conversation https://github.com/JuliaReinforcementLearning/ReinforcementLearning.jl/issues/68 we decided to try to create a common reinforcement learning environment interface with very minimal re…

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## [My own Feedforward Neural Network library :-)](https://discourse.julialang.org/t/my-own-feedforward-neural-network-library/37198)

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**Author:** [@sylvaticus](https://discourse.julialang.org/u/sylvaticus)\
**Replies:** 28\
**Last updated:** [June 15, 2020, 9:03pm UTC](https://discourse.julialang.org/t/my-own-feedforward-neural-network-library/37198 "2020-06-15T21:03:36Z")

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I am learning ML, so I created this toy FNN library… Surely is not optimised like in real ML libraries, but it is already pretty flexible and its simplicity may come on hand in implementing custom solutions… using Ra…

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## [Course indication for programming in Julia](https://discourse.julialang.org/t/course-indication-for-programming-in-julia/41266)

<div class="topic-metadata">

**Author:** [@RaquelSantos](https://discourse.julialang.org/u/RaquelSantos)\
**Replies:** 3\
**Last updated:** [June 15, 2020, 5:25pm UTC](https://discourse.julialang.org/t/course-indication-for-programming-in-julia/41266 "2020-06-15T17:25:00Z")

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I am learning to program in Julia and I would like to indicate specific courses for building linear programming models. Thanks!

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## [How to declare a Boolean variable?](https://discourse.julialang.org/t/how-to-declare-a-boolean-variable/41279)

<div class="topic-metadata">

**Author:** [@RaquelSantos](https://discourse.julialang.org/u/RaquelSantos)\
**Replies:** 4\
**Last updated:** [June 15, 2020, 5:22pm UTC](https://discourse.julialang.org/t/how-to-declare-a-boolean-variable/41279 "2020-06-15T17:22:47Z")

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I need to declare a Boolean variable but I don’t know how to use Bool. How should I do ? I need the variable “i” to assume two values (1, 0) using JuMP, Cbc Model1 = Model(with\_optimizer(Cbc.Optimizer)) @variable(Mode…

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## [Handling unstable true solution issues with the Integrator Interface](https://discourse.julialang.org/t/handling-unstable-true-solution-issues-with-the-integrator-interface/41208)

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**Author:** [@Libbum](https://discourse.julialang.org/u/Libbum)\
**Replies:** 7\
**Last updated:** [June 15, 2020, 12:06pm UTC](https://discourse.julialang.org/t/handling-unstable-true-solution-issues-with-the-integrator-interface/41208 "2020-06-15T12:06:19Z")

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Hi All, Working on a problem that has lead me to the Integrator Interface of DifferentialEquations.jl and have ran into something I can’t seem to work out. My case requires my to solve my ODEProblem on a timescale of d…

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## [How to set @variable(m, tau\[1:N\] \>0 ) with JuMP](https://discourse.julialang.org/t/how-to-set-variable-m-tau-1-n-0-with-jump/41244)

<div class="topic-metadata">

**Author:** [@namch](https://discourse.julialang.org/u/namch)\
**Replies:** 4\
**Last updated:** [June 15, 2020, 8:10am UTC](https://discourse.julialang.org/t/how-to-set-variable-m-tau-1-n-0-with-jump/41244 "2020-06-15T08:10:45Z")

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I get an error when trying to set variables larger than zero. Is there any way to over come this? ERROR: LoadError: LoadError: In @variable(m, tau\[1:N\] \> 0): Unknown sense \> Thank you

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## [RHS and LHS inconsistency in indexing over constraints](https://discourse.julialang.org/t/rhs-and-lhs-inconsistency-in-indexing-over-constraints/41409)

<div class="topic-metadata">

**Author:** [@barguzin](https://discourse.julialang.org/u/barguzin)\
**Replies:** 2\
**Last updated:** [June 15, 2020, 1:33am UTC](https://discourse.julialang.org/t/rhs-and-lhs-inconsistency-in-indexing-over-constraints/41409 "2020-06-15T01:33:34Z")

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Hi folks, This is my first time using Julia for math optimization (was previously running Xpress FICO). I am trying to run a relatively easy anti-covering model. But I am running into issue with indices (or something e…

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## [Heat / diffusion equation with co-ordinate dependent diffusion coefficient](https://discourse.julialang.org/t/heat-diffusion-equation-with-co-ordinate-dependent-diffusion-coefficient/41380)

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**Author:** [@Eben60](https://discourse.julialang.org/u/Eben60)\
**Replies:** 7\
**Last updated:** [June 14, 2020, 9:16pm UTC](https://discourse.julialang.org/t/heat-diffusion-equation-with-co-ordinate-dependent-diffusion-coefficient/41380 "2020-06-14T21:16:05Z")

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I am starting with the example at DiffEqOperators . I am interested in the steady state only. Let us have Neumann border condition (physically, a constant source of e.g. heat) on the left, and Dirichlet BC on the right. …

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## [Multidimentional integrals in julia: speed and automatic differentiation](https://discourse.julialang.org/t/multidimentional-integrals-in-julia-speed-and-automatic-differentiation/41375)

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**Author:** [@misha\_mikhasenko](https://discourse.julialang.org/u/misha_mikhasenko)\
**Replies:** 9\
**Last updated:** [June 14, 2020, 8:16pm UTC](https://discourse.julialang.org/t/multidimentional-integrals-in-julia-speed-and-automatic-differentiation/41375 "2020-06-14T20:16:14Z")

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I would like to differentiate through a two-dimensional integral. seems to be not possible for c++ wrappers (e.g. with the great Cuba.jl) Julia native integrators are way slower (HCubature.jl, NIntegration.jl) nested Q…

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## [Different result with PeriodicCallback](https://discourse.julialang.org/t/different-result-with-periodiccallback/41273)

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**Author:** [@ohmsweetohm1](https://discourse.julialang.org/u/ohmsweetohm1)\
**Replies:** 13\
**Last updated:** [June 14, 2020, 4:47pm UTC](https://discourse.julialang.org/t/different-result-with-periodiccallback/41273 "2020-06-14T16:47:34Z")

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I am trieing to understand the PeriodicCallback method and noticed something weird. using DifferentialEquations, PyPlot mutable struct SimType{T} \<: DEDataVector{T} x::Vector{T} a::T end f1(du, u, p, t) = du\[1…

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## [Backpropagation Through Time](https://discourse.julialang.org/t/backpropagation-through-time/40822)

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**Author:** [@Freddy\_Chua](https://discourse.julialang.org/u/Freddy_Chua)\
**Replies:** 1\
**Last updated:** [June 14, 2020, 10:50am UTC](https://discourse.julialang.org/t/backpropagation-through-time/40822 "2020-06-14T10:50:58Z")

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Hi, I noted the used of “record” for BPTT for LSTM/Recurrence based Models. Is this in used? I don’t see it being documented anywhere, i also could not find it in the code. How do we do BPTT?

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## [Eigensolver for interior eigenvalues of sparse (banded) Hermitian matrices?](https://discourse.julialang.org/t/eigensolver-for-interior-eigenvalues-of-sparse-banded-hermitian-matrices/41360)

<div class="topic-metadata">

**Author:** [@Grayscale](https://discourse.julialang.org/u/Grayscale)\
**Replies:** 3\
**Last updated:** [June 14, 2020, 8:54am UTC](https://discourse.julialang.org/t/eigensolver-for-interior-eigenvalues-of-sparse-banded-hermitian-matrices/41360 "2020-06-14T08:54:50Z")

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I am trying to compute many interior eigenvalues of large sparse banded complex Hermitian matrices. By the way, the (absolute value of the) matrix looks like this for the ~1500 by ~1500 case: Here, ~ 98.8% of the el…

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## [Reading parquet very slow](https://discourse.julialang.org/t/reading-parquet-very-slow/41344)

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**Author:** [@freeman](https://discourse.julialang.org/u/freeman)\
**Replies:** 4\
**Last updated:** [June 14, 2020, 8:48am UTC](https://discourse.julialang.org/t/reading-parquet-very-slow/41344 "2020-06-14T08:48:59Z")

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I have a parquet file, about 100mb compressed. In python, reading it with pd.read\_parquet(path) takes about 1 second. The file is 12GB in memory. In Julia this: using DataFrames, ParquetFiles df = DataFrame(lo…

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## [Custom dataset](https://discourse.julialang.org/t/custom-dataset/41329)

<div class="topic-metadata">

**Author:** [@SubhadityaMukherjee](https://discourse.julialang.org/u/SubhadityaMukherjee)\
**Replies:** 2\
**Last updated:** [June 14, 2020, 6:42am UTC](https://discourse.julialang.org/t/custom-dataset/41329 "2020-06-14T06:42:01Z")

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Hello! I am new here. I have been trying to use Metalhead.jl/Flux.jl to train custom image classifiers but I cant seem to be able to load data from a folder directly. (Not part of the standard datasets). Say I have a f…

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## [A question about Plots](https://discourse.julialang.org/t/a-question-about-plots/41311)

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**Author:** [@abcde](https://discourse.julialang.org/u/abcde)\
**Replies:** 3\
**Last updated:** [June 13, 2020, 4:16am UTC](https://discourse.julialang.org/t/a-question-about-plots/41311 "2020-06-13T04:16:52Z")

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The program has run ,but the scatter diagram does not show ,why? Is it too much data in my code?

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## [Add object to existing BSON file?](https://discourse.julialang.org/t/add-object-to-existing-bson-file/41305)

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**Author:** [@e3c6](https://discourse.julialang.org/u/e3c6)\
**Replies:** 1\
**Last updated:** [June 13, 2020, 1:44am UTC](https://discourse.julialang.org/t/add-object-to-existing-bson-file/41305 "2020-06-13T01:44:25Z")

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Suppose I saved a BSON file with BSON.@save "path/to/file.bson" obj1 obj2 . Then later on I create a new obj3 and I want to also add to this file, as if I had executed BSON.@save "path/to/file.bson" obj1 obj2 obj3 …

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## [Implementing recipes on a per package basis?](https://discourse.julialang.org/t/implementing-recipes-on-a-per-package-basis/41198)

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**Author:** [@juliohm](https://discourse.julialang.org/u/juliohm)\
**Replies:** 8\
**Last updated:** [June 12, 2020, 1:24pm UTC](https://discourse.julialang.org/t/implementing-recipes-on-a-per-package-basis/41198 "2020-06-12T13:24:38Z")

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I recently started thinking about an alternative strategy to improving the end user experience in the plotting ecosystem. Is it correct that the recipe system nowadays is decoupled from Plots.jl? For instance, could an a…

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## [Packages to determine confidence intervals](https://discourse.julialang.org/t/packages-to-determine-confidence-intervals/41233)

<div class="topic-metadata">

**Author:** [@feanor12](https://discourse.julialang.org/u/feanor12)\
**Replies:** 1\
**Last updated:** [June 12, 2020, 11:16am UTC](https://discourse.julialang.org/t/packages-to-determine-confidence-intervals/41233 "2020-06-12T11:16:34Z")

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As LsqFit.jl only calculates the standard error by using the Jacobian at the best-fit position I thought I try to write a small package for determining the confidence interval by data exploration. https://github.com/fea…

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## [Gadfly Geom.ribbon bounded left and right - Feature Request](https://discourse.julialang.org/t/gadfly-geom-ribbon-bounded-left-and-right-feature-request/39161)

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**Author:** [@Humphrey\_Lee](https://discourse.julialang.org/u/Humphrey_Lee)\
**Replies:** 2\
**Last updated:** [June 12, 2020, 1:12am UTC](https://discourse.julialang.org/t/gadfly-geom-ribbon-bounded-left-and-right-feature-request/39161 "2020-06-12T01:12:06Z")

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Current implementation of Geom.ribbon is to draw a ribbon at the positions in x bounded above and below by ymax and ymin. Is it possible to draw a ribbon at the positions in y bounded left and right by xmax and xmin? T…

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## [LightGraphs: inconsistency between weighted and non-weighted graphs?](https://discourse.julialang.org/t/lightgraphs-inconsistency-between-weighted-and-non-weighted-graphs/41223)

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**Author:** [@gmouts](https://discourse.julialang.org/u/gmouts)\
**Replies:** 7\
**Last updated:** [June 11, 2020, 8:46pm UTC](https://discourse.julialang.org/t/lightgraphs-inconsistency-between-weighted-and-non-weighted-graphs/41223 "2020-06-11T20:46:30Z")

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I want to get the unweighted adjacency matrix from a weighted graph. I thought that weighs gives the weighted adjacency matrix and adjacency\_matrix gives the unweighted adjacency matrix. I found out this is not true: gw…

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## [In place Cholesky solve with zero allocation (simplical vs. supernodal)](https://discourse.julialang.org/t/in-place-cholesky-solve-with-zero-allocation-simplical-vs-supernodal/41115)

<div class="topic-metadata">

**Author:** [@samuelpowell](https://discourse.julialang.org/u/samuelpowell)\
**Replies:** 7\
**Last updated:** [June 11, 2020, 7:16pm UTC](https://discourse.julialang.org/t/in-place-cholesky-solve-with-zero-allocation-simplical-vs-supernodal/41115 "2020-06-11T19:16:43Z")

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I am unable to avoid allocation when performing an in-place solve against a simplical Cholesky factorisation, but have no problems with a supernodal factorisation. Note that: the allocation is small, but since I am pe…

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## [Using Flux to optimize a function of the Singular Values](https://discourse.julialang.org/t/using-flux-to-optimize-a-function-of-the-singular-values/39687)

<div class="topic-metadata">

**Author:** [@rajnrao](https://discourse.julialang.org/u/rajnrao)\
**Replies:** 6\
**Last updated:** [June 11, 2020, 3:04pm UTC](https://discourse.julialang.org/t/using-flux-to-optimize-a-function-of-the-singular-values/39687 "2020-06-11T15:04:13Z")

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Update – using latest Flux. I’d like to optimize a function of the singular values of a matrix. The Flux training loop barfs. Here’s my code using Flux, ForwardDiff, LinearAlgebra, GenericLinearAlgebra m = 20 X = rand…

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## [AmplNLWriter with JuMP 0.21.2](https://discourse.julialang.org/t/amplnlwriter-with-jump-0-21-2/38545)

<div class="topic-metadata">

**Author:** [@noamgold](https://discourse.julialang.org/u/noamgold)\
**Replies:** 13\
**Last updated:** [June 11, 2020, 2:24pm UTC](https://discourse.julialang.org/t/amplnlwriter-with-jump-0-21-2/38545 "2020-06-11T14:24:26Z")

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How to use Couenne (using AmplNLWriter) following the recent changes to the JuMP interface. In particular I am trying m = Model( () → AmplNLSolver(“couenne”) ) and I get the following error: ERROR: LoadError: The pro…

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## [How to obtain numeric arrays from a linear mixed model formula?](https://discourse.julialang.org/t/how-to-obtain-numeric-arrays-from-a-linear-mixed-model-formula/31633)

<div class="topic-metadata">

**Author:** [@kai](https://discourse.julialang.org/u/kai)\
**Replies:** 11\
**Last updated:** [June 11, 2020, 1:54pm UTC](https://discourse.julialang.org/t/how-to-obtain-numeric-arrays-from-a-linear-mixed-model-formula/31633 "2020-06-11T13:54:18Z")

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Hello. I have a data frame (“dat”, with variables x1, y, and id) and a formula (@formula(y ~ 1 + x1 + (1 | id))). I want to obtain the following numeric arrays: y: response vector X: design matrix for fixed effect, wit…

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