# Specific Domains

**URL:** https://discourse.julialang.org/c/domain/10.md?no_subcategories=false&page=544

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**Page:** 545

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## [Group, Mutate, Ungroup](https://discourse.julialang.org/t/group-mutate-ungroup/8819)

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**Author:** [@RandomString123](https://discourse.julialang.org/u/RandomString123)\
**Replies:** 2\
**Last updated:** [February 4, 2018, 11:18pm UTC](https://discourse.julialang.org/t/group-mutate-ungroup/8819 "2018-02-04T23:18:35Z")

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Is there a way developed to support the following workflow? I realize this example is trivial but it could be applied to more complex workflows like subgroup moving averages. And while there are ways to run calculations…

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## [JuMP; Rewriting an @eval @NLexpression with a user defined function in local scope w/ Expr](https://discourse.julialang.org/t/jump-rewriting-an-eval-nlexpression-with-a-user-defined-function-in-local-scope-w-expr/8757)

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**Author:** [@shoshievass](https://discourse.julialang.org/u/shoshievass)\
**Replies:** 6\
**Last updated:** [February 4, 2018, 4:07pm UTC](https://discourse.julialang.org/t/jump-rewriting-an-eval-nlexpression-with-a-user-defined-function-in-local-scope-w-expr/8757 "2018-02-04T16:07:45Z")

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I’m trying to use a user-defined function that takes in several distinct arguments, and then a splatted N-dim vector of parameters as an @NLexpression to be used in a constraint of an optimization problem. I described t…

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## [Parallel Map/Reduce with RemoteChannels - comments on MWE?](https://discourse.julialang.org/t/parallel-map-reduce-with-remotechannels-comments-on-mwe/8761)

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**Author:** [@pasha](https://discourse.julialang.org/u/pasha)\
**Replies:** 3\
**Last updated:** [February 3, 2018, 11:40pm UTC](https://discourse.julialang.org/t/parallel-map-reduce-with-remotechannels-comments-on-mwe/8761 "2018-02-03T23:40:18Z")

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Greetings, I’m working on a project that is a candidate for parallel map/reduce. So, I wrote a MWE of a framework for doing that below, using RemoteChannels and remote\_do(), and am interested in feedback. I’m just com…

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## [A Julian function interpolation library?](https://discourse.julialang.org/t/a-julian-function-interpolation-library/8721)

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**Author:** [@MaximilianJHuber](https://discourse.julialang.org/u/MaximilianJHuber)\
**Replies:** 5\
**Last updated:** [February 3, 2018, 8:45am UTC](https://discourse.julialang.org/t/a-julian-function-interpolation-library/8721 "2018-02-03T08:45:27Z")

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When you want to interpolate a function (match its values on some grid points and approximate it off grid) you: Generate a matrix with evaluations of basis function on the grid and find a linear combination of those th…

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## [Build issues of Ipopt](https://discourse.julialang.org/t/build-issues-of-ipopt/7095)

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**Author:** [@Rahul\_Sharma](https://discourse.julialang.org/u/Rahul_Sharma)\
**Replies:** 4\
**Last updated:** [February 2, 2018, 9:13am UTC](https://discourse.julialang.org/t/build-issues-of-ipopt/7095 "2018-02-02T09:13:49Z")

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Hi all, I am trying to install CoinOptServces package. But, the Ipopt package in it has build issues. It seems that the process ./get.Blas had an error (ProcessExited(1)). How do I install the package without any probe…

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## [JuMP User-Defined Function, Value and Gradient At Once](https://discourse.julialang.org/t/jump-user-defined-function-value-and-gradient-at-once/8681)

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**Author:** [@nhipsman](https://discourse.julialang.org/u/nhipsman)\
**Replies:** 3\
**Last updated:** [February 1, 2018, 8:27pm UTC](https://discourse.julialang.org/t/jump-user-defined-function-value-and-gradient-at-once/8681 "2018-02-01T20:27:26Z")

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Hi - I have a user-defined function for which I have an analytical gradient I’d like to use. Furthermore, most of the effort in calculating that gradient is already done in calculating the value of the function. Is th…

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## [Concatenate CSV data into Feather using DataStreams](https://discourse.julialang.org/t/concatenate-csv-data-into-feather-using-datastreams/3690)

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**Author:** [@Tamas\_Papp](https://discourse.julialang.org/u/Tamas_Papp)\
**Replies:** 5\
**Last updated:** [February 1, 2018, 6:50am UTC](https://discourse.julialang.org/t/concatenate-csv-data-into-feather-using-datastreams/3690 "2018-02-01T06:50:32Z")

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I have about 400G of data in 15 .csv.gz files, overall 2e9 records with 20 columns, same schema in each file. I would like to read all of them and save in a single .feather file for further analysis. I could not figure …

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## [Stochastic solver pushes chemical langevin equations into negative concentrations](https://discourse.julialang.org/t/stochastic-solver-pushes-chemical-langevin-equations-into-negative-concentrations/8688)

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**Author:** [@Torkel](https://discourse.julialang.org/u/Torkel)\
**Replies:** 3\
**Last updated:** [January 31, 2018, 2:08pm UTC](https://discourse.julialang.org/t/stochastic-solver-pushes-chemical-langevin-equations-into-negative-concentrations/8688 "2018-01-31T14:08:14Z")

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Summary: When I simulate the stochastic time development of a reaction network the simulation crashes due to concentrations becoming negative (works fine for deterministic solution). I have this chemical reaction networ…

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## [Correct way to express SOSII constraints](https://discourse.julialang.org/t/correct-way-to-express-sosii-constraints/8596)

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**Author:** [@michaellindon](https://discourse.julialang.org/u/michaellindon)\
**Replies:** 8\
**Last updated:** [January 31, 2018, 3:46am UTC](https://discourse.julialang.org/t/correct-way-to-express-sosii-constraints/8596 "2018-01-31T03:46:19Z")

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I have an application in which I would like to use SOS II constraints to model a piecewise linear approximation to non-linear function. In particular I have a log(z) term in my objective which I would like to approximate…

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## [Thread lock with async channel?](https://discourse.julialang.org/t/thread-lock-with-async-channel/8674)

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**Author:** [@jwu](https://discourse.julialang.org/u/jwu)\
**Replies:** 2\
**Last updated:** [January 31, 2018, 3:37am UTC](https://discourse.julialang.org/t/thread-lock-with-async-channel/8674 "2018-01-31T03:37:25Z")

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The @threads seems not working well with async channel. the following code blocks forever, is there something wrong? using Base.Threads c = Channel{Int}(1) mutex = SpinLock() @sync begin @async begin # …

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## [Various by-group strategies compared](https://discourse.julialang.org/t/various-by-group-strategies-compared/6594)

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**Author:** [@xiaodai](https://discourse.julialang.org/u/xiaodai)\
**Replies:** 36\
**Last updated:** [January 30, 2018, 11:28pm UTC](https://discourse.julialang.org/t/various-by-group-strategies-compared/6594 "2018-01-30T23:28:40Z")

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Update 12th Nov 2017 2nd Update Implemented a multi-threaded that is almost 2x faster than data.table! Implemented a new radixgroup that is even faster than the previous method by 18% on 250 million element arrays. Up…

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## [Julia Support for File Loading](https://discourse.julialang.org/t/julia-support-for-file-loading/8673)

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**Author:** [@RandomString123](https://discourse.julialang.org/u/RandomString123)\
**Replies:** 22\
**Last updated:** [January 30, 2018, 2:07pm UTC](https://discourse.julialang.org/t/julia-support-for-file-loading/8673 "2018-01-30T14:07:58Z")

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As a first learning project in Julia I have started to try to convert a project I did in R into Julia. And it turns out I quickly ran into a couple roadblocks. All of which are related to reading in legacy data files l…

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## [Replicating a useful Stata Workflow with DataFramesMeta](https://discourse.julialang.org/t/replicating-a-useful-stata-workflow-with-dataframesmeta/8671)

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**Author:** [@pdeffebach](https://discourse.julialang.org/u/pdeffebach)\
**Replies:** 6\
**Last updated:** [January 30, 2018, 2:07pm UTC](https://discourse.julialang.org/t/replicating-a-useful-stata-workflow-with-dataframesmeta/8671 "2018-01-30T14:07:20Z")

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One thing that is necessary when working with survey data is being able create new variables by standardizing capping existing variables variables. One workflow might look like this: sysuse auto local variables\_to\_cap …

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## [Convex.jl: Return number of solver iterations](https://discourse.julialang.org/t/convex-jl-return-number-of-solver-iterations/8689)

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**Author:** [@migarstka](https://discourse.julialang.org/u/migarstka)\
**Replies:** 0\
**Last updated:** [January 30, 2018, 12:17pm UTC](https://discourse.julialang.org/t/convex-jl-return-number-of-solver-iterations/8689 "2018-01-30T12:17:23Z")

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Hi, is there any way to return the number of solver iterations to convergence when I solve an optimization problem with Convex.jl and the SCS-solver? Thank you!

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## [Linking axes](https://discourse.julialang.org/t/linking-axes/8633)

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**Author:** [@airpmb](https://discourse.julialang.org/u/airpmb)\
**Replies:** 8\
**Last updated:** [January 29, 2018, 11:01pm UTC](https://discourse.julialang.org/t/linking-axes/8633 "2018-01-29T23:01:07Z")

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Do any of the plotting packages for Julia support linking the axes of plots, as well as interactive zooming/panning? I’ve found mention (though not in docs, only in GitHub issues) of a link kwarg in Plots.jl, but it didn…

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## [JuMP (Not) Passing Exact Hessians to Ipopt](https://discourse.julialang.org/t/jump-not-passing-exact-hessians-to-ipopt/7844)

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**Author:** [@Juser](https://discourse.julialang.org/u/Juser)\
**Replies:** 12\
**Last updated:** [January 29, 2018, 10:17pm UTC](https://discourse.julialang.org/t/jump-not-passing-exact-hessians-to-ipopt/7844 "2018-01-29T22:17:30Z")

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When using Ipopt through JuMP, I find myself unable to set hessian\_approximation=“exact” (i.e. to tell Ipopt that I will give it an exact hessian). When I try, I get an error to the effect of “Exception message: eval\_h…

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## [Nonlinear Constraints with Splatting](https://discourse.julialang.org/t/nonlinear-constraints-with-splatting/8677)

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**Author:** [@shoshievass](https://discourse.julialang.org/u/shoshievass)\
**Replies:** 7\
**Last updated:** [January 29, 2018, 9:47pm UTC](https://discourse.julialang.org/t/nonlinear-constraints-with-splatting/8677 "2018-01-29T21:47:05Z")

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I’m trying to solve an optimization problem w/ (N+1) parameters subject to a set of N nonlinear constraints, each of which relies on the whole vector of the parameters. A simplified version of my problem looks like this…

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## [Progress towards faster \`sortperm\` for Strings](https://discourse.julialang.org/t/progress-towards-faster-sortperm-for-strings/8505)

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**Author:** [@xiaodai](https://discourse.julialang.org/u/xiaodai)\
**Replies:** 16\
**Last updated:** [January 29, 2018, 4:45am UTC](https://discourse.julialang.org/t/progress-towards-faster-sortperm-for-strings/8505 "2018-01-29T04:45:39Z")

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I have just implemented an idea I had to make sortperm faster for Strings. It is implemented in SortingLab.jl’s fsortperm; and I got the performance on a particular benchmark to be 7x faster than Base.sortperm, see code …

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## [NLopt 0.3.6 segfaults Julia 0.6.2](https://discourse.julialang.org/t/nlopt-0-3-6-segfaults-julia-0-6-2/8645)

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**Author:** [@ivo\_welch](https://discourse.julialang.org/u/ivo_welch)\
**Replies:** 0\
**Last updated:** [January 27, 2018, 9:54pm UTC](https://discourse.julialang.org/t/nlopt-0-3-6-segfaults-julia-0-6-2/8645 "2018-01-27T21:54:54Z")

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julia\> using NLopt julia\> myfun(x::Vector, unused::Vector)= (x\[1\]-2)^2 + (x\[2\]-3)^2 + (x\[1\]\*x\[2\])^2 myfun (generic function with 1 method) julia\> opt= Opt(:LN\_NELDERMEAD,2) Opt(:LN\_NELDERMEAD, 2) julia\> lower\_bounds!(…

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## [Optim L-BFGS() - Can I save internal state?](https://discourse.julialang.org/t/optim-l-bfgs-can-i-save-internal-state/8583)

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**Author:** [@egcjm](https://discourse.julialang.org/u/egcjm)\
**Replies:** 1\
**Last updated:** [January 25, 2018, 11:32am UTC](https://discourse.julialang.org/t/optim-l-bfgs-can-i-save-internal-state/8583 "2018-01-25T11:32:52Z")

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Oftentimes, L-BFGS has not converged when it stops after a few hours of crunching away because I specified too few iterations… I then would like to continue without having to restart from scratch, i.e. without L-BFGS reb…

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## [optim arguments: higher dimensional arrays and gradient specification](https://discourse.julialang.org/t/optim-arguments-higher-dimensional-arrays-and-gradient-specification/8500)

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**Author:** [@egcjm](https://discourse.julialang.org/u/egcjm)\
**Replies:** 10\
**Last updated:** [January 26, 2018, 2:31pm UTC](https://discourse.julialang.org/t/optim-arguments-higher-dimensional-arrays-and-gradient-specification/8500 "2018-01-26T14:31:30Z")

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Two questions regarding optim,jl: Gradient specification for higher dimensional arrays. Optim.jl documentation states that “for zeroth and first order methods, it is also possible to pass in matrices, or even higher d…

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## [On Machine Learning and Programming Languages](https://discourse.julialang.org/t/on-machine-learning-and-programming-languages/7574)

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**Author:** [@Mason](https://discourse.julialang.org/u/Mason)\
**Replies:** 48\
**Last updated:** [January 25, 2018, 3:50pm UTC](https://discourse.julialang.org/t/on-machine-learning-and-programming-languages/7574 "2018-01-25T15:50:52Z")

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New blog post on the Julia website

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## [Help with eigenvalue decomposition for symmetric matrices](https://discourse.julialang.org/t/help-with-eigenvalue-decomposition-for-symmetric-matrices/8272)

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**Author:** [@MarioSouto](https://discourse.julialang.org/u/MarioSouto)\
**Replies:** 2\
**Last updated:** [January 25, 2018, 3:17pm UTC](https://discourse.julialang.org/t/help-with-eigenvalue-decomposition-for-symmetric-matrices/8272 "2018-01-25T15:17:47Z")

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Dear all, For some reason Julia’s eigenvalue factorization for symmetric matrices is considerable slow in my machine (MacBook Air, 1.8 GHz Intel Core i5, 4 GB 1600 MHz DDR3). In this same machine, Scipy’s eigenvalue fac…

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## [Julia Script running with SQL datas](https://discourse.julialang.org/t/julia-script-running-with-sql-datas/8566)

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**Author:** [@fenosoa](https://discourse.julialang.org/u/fenosoa)\
**Replies:** 5\
**Last updated:** [January 24, 2018, 10:44pm UTC](https://discourse.julialang.org/t/julia-script-running-with-sql-datas/8566 "2018-01-24T22:44:35Z")

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Hi, I’m currently working on a web app for a college. In this app, students have to rank a list of classes (front in React). Datas and rankings are send to a Node.js - MySQL - Sequelize backend, and we found a .jl algor…

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## [Equivalent for tf.keras.layers.Lambda in Tensorflow.jl/MXNet.jl](https://discourse.julialang.org/t/equivalent-for-tf-keras-layers-lambda-in-tensorflow-jl-mxnet-jl/8511)

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**Author:** [@v-i-s-h](https://discourse.julialang.org/u/v-i-s-h)\
**Replies:** 1\
**Last updated:** [January 24, 2018, 4:55pm UTC](https://discourse.julialang.org/t/equivalent-for-tf-keras-layers-lambda-in-tensorflow-jl-mxnet-jl/8511 "2018-01-24T16:55:44Z")

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Hi, I’m porting some code from Python using Tensorflow to Julia. I’m unable to find an equivalent for custom layer in TensorFlow.jl or in MXNet.jl. This is the exact code I want to translate: from tensorflow.python.ke…

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## [Converting Float32 to N0f32 in FixedPointNumbers.jl](https://discourse.julialang.org/t/converting-float32-to-n0f32-in-fixedpointnumbers-jl/8555)

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**Author:** [@jwu](https://discourse.julialang.org/u/jwu)\
**Replies:** 2\
**Last updated:** [January 24, 2018, 4:22pm UTC](https://discourse.julialang.org/t/converting-float32-to-n0f32-in-fixedpointnumbers-jl/8555 "2018-01-24T16:22:57Z")

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this works in Julia 0.6.2: Float32(1.0) |\> N0f8 Float32(1.0) |\> N0f16 this will not work Float32(1.0) |\> N0f32 Float32(1.0) |\> N0f64 Float64(1.0) |\> N0f64 It looks like when the number of bits is the same or larger, …

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## [Linking solver binaries with models (JuMP)](https://discourse.julialang.org/t/linking-solver-binaries-with-models-jump/8453)

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**Author:** [@Curious1](https://discourse.julialang.org/u/Curious1)\
**Replies:** 7\
**Last updated:** [January 24, 2018, 11:43am UTC](https://discourse.julialang.org/t/linking-solver-binaries-with-models-jump/8453 "2018-01-24T11:43:57Z")

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I have binaries of solvers in a particular directory of my linux systems. Now I want to solve my JuMP model using those binaries. How do I do that?

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## [TeaPot like thing in Julia](https://discourse.julialang.org/t/teapot-like-thing-in-julia/8561)

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**Author:** [@Arshpreet\_Singh](https://discourse.julialang.org/u/Arshpreet_Singh)\
**Replies:** 0\
**Last updated:** [January 24, 2018, 11:04am UTC](https://discourse.julialang.org/t/teapot-like-thing-in-julia/8561 "2018-01-24T11:04:22Z")

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I was looking for Teapot like in Julia. Here is Teapot in Python: To summarize what we’ve learned so far about effective machine learning system design, we should: Always tune the hyperparameters for our models Always…

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## [Rationalize() error](https://discourse.julialang.org/t/rationalize-error/8544)

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**Author:** [@Yaroslav\_Kavenchuk](https://discourse.julialang.org/u/Yaroslav_Kavenchuk)\
**Replies:** 2\
**Last updated:** [January 23, 2018, 9:34pm UTC](https://discourse.julialang.org/t/rationalize-error/8544 "2018-01-23T21:34:56Z")

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\_ \_ \_ \_(\_)\_ | A fresh approach to technical computing (\_) | (\_) (\_) | Documentation: https://docs.julialang.org \_ \_ \_| |\_ \_\_ \_ | Type "?help" for help. | | | | | | |/ \_\` …

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## [Rounding off error in simple calculations](https://discourse.julialang.org/t/rounding-off-error-in-simple-calculations/8543)

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**Author:** [@sambitdash](https://discourse.julialang.org/u/sambitdash)\
**Replies:** 3\
**Last updated:** [January 23, 2018, 12:34pm UTC](https://discourse.julialang.org/t/rounding-off-error-in-simple-calculations/8543 "2018-01-23T12:34:23Z")

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julia\> 2.5/3 0.8333333333333334 The result should have been reported 0.8333333333333333. An infinite series of 3s will never reach to 4 and will be a floor when rounded. Is there any specific reason we have preferred r…

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