# Specific Domains

**URL:** https://discourse.julialang.org/c/domain/10.md?no_subcategories=false&page=483

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**Page:** 484

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## [Group-by performance benchmarks and recommendations](https://discourse.julialang.org/t/group-by-performance-benchmarks-and-recommendations/9313)

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**Author:** [@xiaodai](https://discourse.julialang.org/u/xiaodai)\
**Replies:** 12\
**Last updated:** [September 2, 2019, 9:58pm UTC](https://discourse.julialang.org/t/group-by-performance-benchmarks-and-recommendations/9313 "2019-09-02T21:58:48Z")

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I have been trying to improve Julia’s DataFrame group-by for a while now and I think I am able to synthesized my thinking into APIs. Here are my synthesized recommendation (as of 25th Feb 2018) Recommendation Why? B…

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## [Read and write/save 3-D image](https://discourse.julialang.org/t/read-and-write-save-3-d-image/26978)

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**Author:** [@Yoshua](https://discourse.julialang.org/u/Yoshua)\
**Replies:** 5\
**Last updated:** [September 2, 2019, 9:50pm UTC](https://discourse.julialang.org/t/read-and-write-save-3-d-image/26978 "2019-09-02T21:50:33Z")

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Hello! I have problem with image manipulation. I want to save a 3D image array in png format. Also wanted to know how to plot an image with some function of ImageView or Image package. Image encoding is RGB. If anyon…

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## [How to use Flux.train! to train custom layer?](https://discourse.julialang.org/t/how-to-use-flux-train-to-train-custom-layer/28293)

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**Author:** [@zhangqian](https://discourse.julialang.org/u/zhangqian)\
**Replies:** 2\
**Last updated:** [September 2, 2019, 6:45pm UTC](https://discourse.julialang.org/t/how-to-use-flux-train-to-train-custom-layer/28293 "2019-09-02T18:45:13Z")

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Hi I am trying to build a toy custom layer according to the instruction from Building Layers (Basics · Flux) in Basics · Flux, and train it with the train! method in Flux.jl. However, the loss does not decrease and the …

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## [Animation fails in frame()](https://discourse.julialang.org/t/animation-fails-in-frame/28022)

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**Author:** [@Brad\_Hines](https://discourse.julialang.org/u/Brad_Hines)\
**Replies:** 9\
**Last updated:** [September 2, 2019, 7:35am UTC](https://discourse.julialang.org/t/animation-fails-in-frame/28022 "2019-09-02T07:35:48Z")

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I am trying to build an animation from a double-loop that goes through every hour then every minute of a day, constructing a simulated image. When my code gets to this line: Plots.frame(anim,plt) it dies with the erro…

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## [First part benchmarking medium-data tools](https://discourse.julialang.org/t/first-part-benchmarking-medium-data-tools/28260)

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**Author:** [@xiaodai](https://discourse.julialang.org/u/xiaodai)\
**Replies:** 4\
**Last updated:** [September 1, 2019, 9:41pm UTC](https://discourse.julialang.org/t/first-part-benchmarking-medium-data-tools/28260 "2019-09-01T21:41:51Z")

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I compared and contrast JuliaDB with Dask and disk.frame. http://diskframe.com/articles/vs-dask-juliadb.html Probably more to come, but JuliaDB needs to mature before it can be a contender in these benchmarks.

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## [How to build CDDLib.jl on Windows ✅](https://discourse.julialang.org/t/how-to-build-cddlib-jl-on-windows/28114)

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**Author:** [@uwechsler](https://discourse.julialang.org/u/uwechsler)\
**Replies:** 1\
**Last updated:** [September 1, 2019, 2:48pm UTC](https://discourse.julialang.org/t/how-to-build-cddlib-jl-on-windows/28114 "2019-09-01T14:48:16Z")

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For my current project, I’d like to run CDDLib.jl on a Windows system. Currently, I get the following error message when trying to build the library. (v1.1) pkg\> build CDDLib Building SpecialFunctions → \`C:\\Users\\wue…

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## [CRAM support?](https://discourse.julialang.org/t/cram-support/28222)

<div class="topic-metadata">

**Author:** [@brendanofallon](https://discourse.julialang.org/u/brendanofallon)\
**Replies:** 5\
**Last updated:** [September 1, 2019, 2:10pm UTC](https://discourse.julialang.org/t/cram-support/28222 "2019-09-01T14:10:56Z")

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Hello, I’m wondering if there’s support, or plans for support, of the CRAM alignment format in BioJulia? I didn’t come across anything obvious reading the documentation, but perhaps it’s hiding somewhere, or a work in pr…

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## [Most efficient way to compute number of rows in each group using JuliaDB?](https://discourse.julialang.org/t/most-efficient-way-to-compute-number-of-rows-in-each-group-using-juliadb/28256)

<div class="topic-metadata">

**Author:** [@xiaodai](https://discourse.julialang.org/u/xiaodai)\
**Replies:** 0\
**Last updated:** [September 1, 2019, 8:01am UTC](https://discourse.julialang.org/t/most-efficient-way-to-compute-number-of-rows-in-each-group-using-juliadb/28256 "2019-09-01T08:01:37Z")

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Suppose a is a JuliaDB table, is the below the best (most efficient) way to compute the number of rows per group? using LambdaFn, DataFrames, JuliaDB a = DataFrame(Column1 = rand(\["a", "b", "c"\], 1\_000), b = rand(1000))…

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## [How do I fit a distribution to these data sets?!](https://discourse.julialang.org/t/how-do-i-fit-a-distribution-to-these-data-sets/28243)

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**Author:** [@mthelm85](https://discourse.julialang.org/u/mthelm85)\
**Replies:** 5\
**Last updated:** [September 1, 2019, 5:59am UTC](https://discourse.julialang.org/t/how-do-i-fit-a-distribution-to-these-data-sets/28243 "2019-09-01T05:59:22Z")

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Let me start by saying that I’m very inexperienced in this area, so go easy on me @Tamas\_Papp :wink:. I have two datasets that are similar in shape and I’m trying to fit a distribution to each of them with the goal of be…

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## [Trying to analyse Fannie Mae data with JuliaDB](https://discourse.julialang.org/t/trying-to-analyse-fannie-mae-data-with-juliadb/21410)

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**Author:** [@xiaodai](https://discourse.julialang.org/u/xiaodai)\
**Replies:** 14\
**Last updated:** [August 31, 2019, 11:27pm UTC](https://discourse.julialang.org/t/trying-to-analyse-fannie-mae-data-with-juliadb/21410 "2019-08-31T23:27:45Z")

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I am doing my best to analyse Fannie Mae data with JuliaDB. However the f First Step is to download the Fannie Mae Data and unzip them all Now I tried to load the data using loadtable but it didn’t work. So I split th…

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## [Comparison between time taken in Python and Julia](https://discourse.julialang.org/t/comparison-between-time-taken-in-python-and-julia/28159)

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**Author:** [@richie96](https://discourse.julialang.org/u/richie96)\
**Replies:** 2\
**Last updated:** [August 29, 2019, 11:39am UTC](https://discourse.julialang.org/t/comparison-between-time-taken-in-python-and-julia/28159 "2019-08-29T11:39:04Z")

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Hi, I am doing a comparison between Python and Julia by analyzing the same data set. I am using a data set containing nearly 800,000 rows of data. I load the data from two csv files containing equal amount of data each…

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## [Mixedmodels.jl branches: nlmm and dropmulαβ!](https://discourse.julialang.org/t/mixedmodels-jl-branches-nlmm-and-dropmul/28223)

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**Author:** [@Juan](https://discourse.julialang.org/u/Juan)\
**Replies:** 2\
**Last updated:** [August 31, 2019, 11:48am UTC](https://discourse.julialang.org/t/mixedmodels-jl-branches-nlmm-and-dropmul/28223 "2019-08-31T11:48:43Z")

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I’ve seen the Mixedmodels.jl package has thre differente branches: master nlmm dropmulαβ! How are they different? What’s new there?

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## [GLM linear regression. How to extract the coefficients?](https://discourse.julialang.org/t/glm-linear-regression-how-to-extract-the-coefficients/28219)

<div class="topic-metadata">

**Author:** [@doomphoenix-qxz](https://discourse.julialang.org/u/doomphoenix-qxz)\
**Replies:** 3\
**Last updated:** [August 30, 2019, 9:56pm UTC](https://discourse.julialang.org/t/glm-linear-regression-how-to-extract-the-coefficients/28219 "2019-08-30T21:56:45Z")

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I fit a simple linear regression using GLM. How do I extract the calculated slope and intercept? I looked through the documentation but didn’t see an example of it. If such an example exists, feel free to point there.

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## [Parallel computing using Parallel Ensemble Simulations (DiffEq) does not seem to work](https://discourse.julialang.org/t/parallel-computing-using-parallel-ensemble-simulations-diffeq-does-not-seem-to-work/28115)

<div class="topic-metadata">

**Author:** [@Torkel](https://discourse.julialang.org/u/Torkel)\
**Replies:** 13\
**Last updated:** [August 30, 2019, 2:18pm UTC](https://discourse.julialang.org/t/parallel-computing-using-parallel-ensemble-simulations-diffeq-does-not-seem-to-work/28115 "2019-08-30T14:18:23Z")

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So i regularly run SDE simulations. To get a better idea of the systems behavior I would run several identical, and plot the various results. I figured this probably would be a good task for the Parallel Ensemble Simulat…

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## [BFloat16 on ARM for neural networks](https://discourse.julialang.org/t/bfloat16-on-arm-for-neural-networks/28200)

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**Author:** [@johnh](https://discourse.julialang.org/u/johnh)\
**Replies:** 1\
**Last updated:** [August 30, 2019, 9:56am UTC](https://discourse.julialang.org/t/bfloat16-on-arm-for-neural-networks/28200 "2019-08-30T09:56:19Z")

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How does this play with Julia? Someone will now tell me thereis a BFlaot16 type in core already!

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## [Power Balance reference in PowerModels.jl](https://discourse.julialang.org/t/power-balance-reference-in-powermodels-jl/27865)

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**Author:** [@andrewrosemberg](https://discourse.julialang.org/u/andrewrosemberg)\
**Replies:** 5\
**Last updated:** [August 30, 2019, 4:19am UTC](https://discourse.julialang.org/t/power-balance-reference-in-powermodels-jl/27865 "2019-08-30T04:19:20Z")

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I’m running an OPF problem with SDPWRMForm and SOCWRConicForm formulations (AbstractWForms) and I’m trying to retrieve the duals from the power balance constraints (lam\_kcl\_r in the output). However, it seams that the re…

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## [Problem in Power Flow using Julia](https://discourse.julialang.org/t/problem-in-power-flow-using-julia/1491)

<div class="topic-metadata">

**Author:** [@ashefa](https://discourse.julialang.org/u/ashefa)\
**Replies:** 18\
**Last updated:** [August 29, 2019, 4:18pm UTC](https://discourse.julialang.org/t/problem-in-power-flow-using-julia/1491 "2019-08-29T16:18:02Z")

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I started writing “Power Flow” in two software, GAMS and Julialang, simultaneously. In addition to i did “Power Flow” in GAMS, i receive to results of “State Estimation” problem, but in Julia (using JuMP) yet i couldn’t …

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## [Makie - drawing lines through transparent surface](https://discourse.julialang.org/t/makie-drawing-lines-through-transparent-surface/28148)

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**Author:** [@nhardy](https://discourse.julialang.org/u/nhardy)\
**Replies:** 4\
**Last updated:** [August 29, 2019, 3:10pm UTC](https://discourse.julialang.org/t/makie-drawing-lines-through-transparent-surface/28148 "2019-08-29T15:10:28Z")

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Hi, I’ve been using Julia and the Plots package for a while, but only recently have tried using Makie for some visualizations, and ran into some problems. No matter what I try, I can’t get line segments to play nicely wi…

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## [How to quickly bulk insert into postgres 1](https://discourse.julialang.org/t/how-to-quickly-bulk-insert-into-postgres-1/27784)

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**Author:** [@datnt2509](https://discourse.julialang.org/u/datnt2509)\
**Replies:** 3\
**Last updated:** [August 29, 2019, 2:12pm UTC](https://discourse.julialang.org/t/how-to-quickly-bulk-insert-into-postgres-1/27784 "2019-08-29T14:12:54Z")

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This is sort of a shot in the dark, I don’t have any reason to believe there’s a better solution to this but I thought I’d give it a try. I’m trying to insert data into tables on a postgres database. I’m using the excel…

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## [ForwardDiff & mul!()](https://discourse.julialang.org/t/forwarddiff-mul/28144)

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**Author:** [@PharmCat](https://discourse.julialang.org/u/PharmCat)\
**Replies:** 6\
**Last updated:** [August 29, 2019, 10:38am UTC](https://discourse.julialang.org/t/forwarddiff-mul/28144 "2019-08-29T10:38:10Z")

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Is it possible to make ForwardDiff works with mul!() inside function? Or how to optimize allocations when I try to get gradient/hessian of likelihood function?

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## [How to "print" a dataframe representation in a string?](https://discourse.julialang.org/t/how-to-print-a-dataframe-representation-in-a-string/28155)

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**Author:** [@sylvaticus](https://discourse.julialang.org/u/sylvaticus)\
**Replies:** 3\
**Last updated:** [August 29, 2019, 9:22am UTC](https://discourse.julialang.org/t/how-to-print-a-dataframe-representation-in-a-string/28155 "2019-08-29T09:22:05Z")

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How do I “print” a representation of a dataframe in within a String, e.g. this would not work: df = DataFrame(c1=\["a","b"\],c2=\[1,2\]) myStr = """ My dataframe: $(show(df,allrows=true, allcols=true)) bla,bla,bla... """

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## [Sample size calculation + experimental design](https://discourse.julialang.org/t/sample-size-calculation-experimental-design/27433)

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**Author:** [@Crghilardi](https://discourse.julialang.org/u/Crghilardi)\
**Replies:** 1\
**Last updated:** [August 28, 2019, 11:35pm UTC](https://discourse.julialang.org/t/sample-size-calculation-experimental-design/27433 "2019-08-28T23:35:32Z")

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I started to write a small function that I use somewhat regularly to calculate sample size from coefficient of variation. I checked JuliaStats/StatsBase to see if any sample size functionality was included and I did not …

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## [Reading .csv.gz with CSV does not find readavailable(::GZipStream)](https://discourse.julialang.org/t/reading-csv-gz-with-csv-does-not-find-readavailable-gzipstream/27966)

<div class="topic-metadata">

**Author:** [@hmmueller](https://discourse.julialang.org/u/hmmueller)\
**Replies:** 4\
**Last updated:** [August 28, 2019, 5:49pm UTC](https://discourse.julialang.org/t/reading-csv-gz-with-csv-does-not-find-readavailable-gzipstream/27966 "2019-08-28T17:49:38Z")

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I had an original piece of code like this, which worked nicely: filepaths = \[joinpath(root, f) for (root, dirs, files) in walkdir(root) for f in files\[occursin.(fnfeature,…

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## [Accumulating distributed data](https://discourse.julialang.org/t/accumulating-distributed-data/28117)

<div class="topic-metadata">

**Author:** [@grahamas](https://discourse.julialang.org/u/grahamas)\
**Replies:** 0\
**Last updated:** [August 28, 2019, 3:56pm UTC](https://discourse.julialang.org/t/accumulating-distributed-data/28117 "2019-08-28T15:56:52Z")

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I’m running distributed simulations and hoping to save the results as I go – the aggregate results are too big to hold in memory. Can someone point me to a good way to do this that doesn’t amount to saving each run in a…

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## [Type VariableRef has no field head](https://discourse.julialang.org/t/type-variableref-has-no-field-head/28116)

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**Author:** [@faoh](https://discourse.julialang.org/u/faoh)\
**Replies:** 0\
**Last updated:** [August 28, 2019, 3:50pm UTC](https://discourse.julialang.org/t/type-variableref-has-no-field-head/28116 "2019-08-28T15:50:18Z")

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Hi All, I try to formulate an objective function, like x\*log(x), x is a nonlinear expression. However, when I run the optimization, it shows type VariableRef has no field head. Anyone else saw this message? JuMP.@NLex…

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## [\[Flux\] Issue while computing Hessian MethodError: objects of type Tracker.Grads are not callable](https://discourse.julialang.org/t/flux-issue-while-computing-hessian-methoderror-objects-of-type-tracker-grads-are-not-callable/27980)

<div class="topic-metadata">

**Author:** [@stochastic\_guy](https://discourse.julialang.org/u/stochastic_guy)\
**Replies:** 12\
**Last updated:** [August 28, 2019, 2:52pm UTC](https://discourse.julialang.org/t/flux-issue-while-computing-hessian-methoderror-objects-of-type-tracker-grads-are-not-callable/27980 "2019-08-28T14:52:23Z")

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I’m new to Flux and I’m trying to compute the hessian. Here’s the code: grad = Flux.gradient(() -\> loss(x, y), Flux.params(model)) hess = Flux.gradient(grad, Flux.params(model)) But when running the line to compute he…

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## [How to easily create graphs from tables?](https://discourse.julialang.org/t/how-to-easily-create-graphs-from-tables/28069)

<div class="topic-metadata">

**Author:** [@Juan](https://discourse.julialang.org/u/Juan)\
**Replies:** 2\
**Last updated:** [August 28, 2019, 8:38am UTC](https://discourse.julialang.org/t/how-to-easily-create-graphs-from-tables/28069 "2019-08-28T08:38:18Z")

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Imagine I have a table with nested levels or a csv file with information like this: (or a little bit more complex with numbers on the right side) fig date kumquat papaya peach …

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## [Knet.jl: Simple MLP for Iris Dataset](https://discourse.julialang.org/t/knet-jl-simple-mlp-for-iris-dataset/24839)

<div class="topic-metadata">

**Author:** [@alasaadstat](https://discourse.julialang.org/u/alasaadstat)\
**Replies:** 6\
**Last updated:** [August 28, 2019, 12:26am UTC](https://discourse.julialang.org/t/knet-jl-simple-mlp-for-iris-dataset/24839 "2019-08-28T00:26:11Z")

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Hi everyone, I’m currently studying (I’m not done reading the docs yet) how Knet works. I’m trying to create a classification model for the iris dataset. That is, using the four features of the iris dataset as the predic…

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## [JuliaDB saving arrays](https://discourse.julialang.org/t/juliadb-saving-arrays/28059)

<div class="topic-metadata">

**Author:** [@grahamas](https://discourse.julialang.org/u/grahamas)\
**Replies:** 1\
**Last updated:** [August 27, 2019, 7:35pm UTC](https://discourse.julialang.org/t/juliadb-saving-arrays/28059 "2019-08-27T19:35:37Z")

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I’m running a parameter sweep solving differential equations and trying to save the results, and have a couple questions: When I try to save a toy example as follows, I get an error that \_impl is not defined for my arg…

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## [ERROR: Package CuArrays errored during testing](https://discourse.julialang.org/t/error-package-cuarrays-errored-during-testing/28006)

<div class="topic-metadata">

**Author:** [@sergevic](https://discourse.julialang.org/u/sergevic)\
**Replies:** 2\
**Last updated:** [August 27, 2019, 4:31pm UTC](https://discourse.julialang.org/t/error-package-cuarrays-errored-during-testing/28006 "2019-08-27T16:31:59Z")

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I followed all the steps in https://juliagpu.gitlab.io/CuArrays.jl/tutorials/generated/intro/ to install Cuda for using it in Julia v. 1.1. I also installed the CUDA Toolkit v. 10.1. After the installation, I run test Cu…

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