# Specific Domains

**URL:** https://discourse.julialang.org/c/domain/10.md?no_subcategories=false&page=466

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**Page:** 467

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## [Solving sparse singular linear systems](https://discourse.julialang.org/t/solving-sparse-singular-linear-systems/33401)

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**Author:** [@FHell](https://discourse.julialang.org/u/FHell)\
**Replies:** 3\
**Last updated:** [January 24, 2020, 1:23pm UTC](https://discourse.julialang.org/t/solving-sparse-singular-linear-systems/33401 "2020-01-24T13:23:19Z")

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I have a problem with solving sparse singular linear systems (flow problems on possibly disconnected graphs). I need the minimum norm solution for this. Essentially the sparse version of this: P = \[0.5, -0.5\] M = \[1. -1…

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## [ArrayFire and FFTW dependency Issue](https://discourse.julialang.org/t/arrayfire-and-fftw-dependency-issue/33735)

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**Author:** [@cshen](https://discourse.julialang.org/u/cshen)\
**Replies:** 0\
**Last updated:** [January 24, 2020, 11:22am UTC](https://discourse.julialang.org/t/arrayfire-and-fftw-dependency-issue/33735 "2020-01-24T11:22:00Z")

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Hello, I’ve been trying to install ArrayFire but there seems to be some issue regarding dependencies regarding FFTW (and Zygote). Here with the most recent FFTW@1.2.0: ERROR: Unsatisfiable requirements detected for p…

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## [Solving for eigenvalues of an equation system in ApproxFun.jl](https://discourse.julialang.org/t/solving-for-eigenvalues-of-an-equation-system-in-approxfun-jl/33682)

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**Author:** [@jbmuir](https://discourse.julialang.org/u/jbmuir)\
**Replies:** 3\
**Last updated:** [January 24, 2020, 11:02am UTC](https://discourse.julialang.org/t/solving-for-eigenvalues-of-an-equation-system-in-approxfun-jl/33682 "2020-01-24T11:02:23Z")

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I’m trying to solve an eigenvalue problem for a system of equations using ApproxFun; however I’m getting an implementation error ERROR: Implement Conversion from Chebyshev{Interval{:closed,:closed,Int64},Float64} to Appr…

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## [Question on behavior with comparisons in MonteCarloMeasurements](https://discourse.julialang.org/t/question-on-behavior-with-comparisons-in-montecarlomeasurements/33679)

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**Author:** [@klaff](https://discourse.julialang.org/u/klaff)\
**Replies:** 7\
**Last updated:** [January 24, 2020, 8:54am UTC](https://discourse.julialang.org/t/question-on-behavior-with-comparisons-in-montecarlomeasurements/33679 "2020-01-24T08:54:35Z")

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I’m playing with MonteCarloMeasurements but running up against limitations around comparisons. julia\> a = Particles(1000, Uniform(0.0,10.0)) Part1000(5.0 ± 2.89) julia\> b = Particles(1000, Uniform(0.0, 10.0)) Part1000(…

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## [Computation of elliptic integrals with arbitrary precision](https://discourse.julialang.org/t/computation-of-elliptic-integrals-with-arbitrary-precision/33717)

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**Author:** [@Gregstrq](https://discourse.julialang.org/u/Gregstrq)\
**Replies:** 1\
**Last updated:** [January 24, 2020, 12:38am UTC](https://discourse.julialang.org/t/computation-of-elliptic-integrals-with-arbitrary-precision/33717 "2020-01-24T00:38:39Z")

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I have seen the issue Support for extended precision in Elliptic.jl. It references the pull request Jacobi elliptic functions and complete elliptic integral of the first kind in SpecialFunctions.jl which is year old and …

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## [Gentler transformation from real to positive](https://discourse.julialang.org/t/gentler-transformation-from-real-to-positive/33695)

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**Author:** [@Tamas\_Papp](https://discourse.julialang.org/u/Tamas_Papp)\
**Replies:** 15\
**Last updated:** [January 23, 2020, 7:54pm UTC](https://discourse.julialang.org/t/gentler-transformation-from-real-to-positive/33695 "2020-01-23T19:54:59Z")

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I am solving an equilibrium of an economic model for prices p \> 0. I need to do this robustly for “wacky” parameter values when I am fitting the model to the data in an outer loop. I have coded up a market clearing resi…

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## [Timings for different groupby approaches](https://discourse.julialang.org/t/timings-for-different-groupby-approaches/33680)

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**Author:** [@venuur](https://discourse.julialang.org/u/venuur)\
**Replies:** 2\
**Last updated:** [January 23, 2020, 2:05am UTC](https://discourse.julialang.org/t/timings-for-different-groupby-approaches/33680 "2020-01-23T02:05:18Z")

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I am running some simulations at work, and I wanted to experiment with different approaches for performing a groupby and then running the simulation. The idea is to run a simulation of each group (identified by an id col…

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## [Interpolation-weighted quadrature rules](https://discourse.julialang.org/t/interpolation-weighted-quadrature-rules/32170)

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**Author:** [@stevengj](https://discourse.julialang.org/u/stevengj)\
**Replies:** 1\
**Last updated:** [January 22, 2020, 8:56pm UTC](https://discourse.julialang.org/t/interpolation-weighted-quadrature-rules/32170 "2020-01-22T20:56:07Z")

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Some of you might be interested in the following notebook, which shows how to construct optimal Gaussian quadrature schemes for arbitrary weight functions constructed from interpolated data: Notes on Solar-Weighted Gau…

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## [COM server for editing Excel files?](https://discourse.julialang.org/t/com-server-for-editing-excel-files/33672)

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**Author:** [@Iulian.Cioarca](https://discourse.julialang.org/u/Iulian.Cioarca)\
**Replies:** 0\
**Last updated:** [January 22, 2020, 7:10pm UTC](https://discourse.julialang.org/t/com-server-for-editing-excel-files/33672 "2020-01-22T19:10:54Z")

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I’m using GitHub - felipenoris/XLSX.jl: Excel file reader and writer for the Julia language. to write data into Excel files and it works great!Thanks,@felipenoris! I would also like to add some formatting(colors, borders…

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## [Interpolated heatmap with contour line in VegaLite.jl](https://discourse.julialang.org/t/interpolated-heatmap-with-contour-line-in-vegalite-jl/33559)

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**Author:** [@affans](https://discourse.julialang.org/u/affans)\
**Replies:** 1\
**Last updated:** [January 22, 2020, 5:48pm UTC](https://discourse.julialang.org/t/interpolated-heatmap-with-contour-line-in-vegalite-jl/33559 "2020-01-22T17:48:38Z")

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Looking to generate a continous heatmap of data, with a contour line, something line the following plot: Example data if someone wants to play with it: delay,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,7…

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## [Create unit from string with Unitful.jl](https://discourse.julialang.org/t/create-unit-from-string-with-unitful-jl/33666)

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**Author:** [@moesphere](https://discourse.julialang.org/u/moesphere)\
**Replies:** 1\
**Last updated:** [January 22, 2020, 4:13pm UTC](https://discourse.julialang.org/t/create-unit-from-string-with-unitful-jl/33666 "2020-01-22T16:13:18Z")

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Is it possible to create a unit from a string with the Unitful.jl package at runtime without using eval? Something like this: unit\_str = "mol/L" unitful\_unit = unit(unit\_str) I only found u"..." and @u\_str, where stri…

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## [Loading of Flux model using BSON: Tracker not found error?](https://discourse.julialang.org/t/loading-of-flux-model-using-bson-tracker-not-found-error/33659)

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**Author:** [@compleat](https://discourse.julialang.org/u/compleat)\
**Replies:** 0\
**Last updated:** [January 22, 2020, 1:12pm UTC](https://discourse.julialang.org/t/loading-of-flux-model-using-bson-tracker-not-found-error/33659 "2020-01-22T13:12:08Z")

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I am having difficulty loading a BSON-saved Flux model via: BSON.@load “my\_model.jls” resulting the error ERROR: LoadError: UndefVarError: Tracker not defined even though I had explicitly loaded Tracker via using Fl…

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## [I've written softmax() function, but I don't get the proper answer](https://discourse.julialang.org/t/ive-written-softmax-function-but-i-dont-get-the-proper-answer/33610)

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**Author:** [@dialektike](https://discourse.julialang.org/u/dialektike)\
**Replies:** 2\
**Last updated:** [January 22, 2020, 4:36am UTC](https://discourse.julialang.org/t/ive-written-softmax-function-but-i-dont-get-the-proper-answer/33610 "2020-01-22T04:36:32Z")

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In order to study ML, I’m making my own softmax () function. I created a softmax () function as follows: function softmax(a) c = maximum(a) exp.(a .- c) / sum(exp.(a .- c)) end The sum of the values in the outp…

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## [\`sol.du\` is \`nothing\` in \`DAESolution\`](https://discourse.julialang.org/t/sol-du-is-nothing-in-daesolution/33636)

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**Author:** [@zekeriya.sari](https://discourse.julialang.org/u/zekeriya.sari)\
**Replies:** 0\
**Last updated:** [January 21, 2020, 8:32pm UTC](https://discourse.julialang.org/t/sol-du-is-nothing-in-daesolution/33636 "2020-01-21T20:32:37Z")

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I tried the DAEProblem example in the manual of the DifferentialEquations. The example is given is here. using DifferentialEquations using Sundials function f(out,du,u,p,t) out\[1\] = - 0.04u\[1\] + 1e4\*u\[2\]…

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## [MINLP optimization with user defined objective function](https://discourse.julialang.org/t/minlp-optimization-with-user-defined-objective-function/33627)

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**Author:** [@martina](https://discourse.julialang.org/u/martina)\
**Replies:** 3\
**Last updated:** [January 21, 2020, 4:45pm UTC](https://discourse.julialang.org/t/minlp-optimization-with-user-defined-objective-function/33627 "2020-01-21T16:45:37Z")

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Hello, I’m still very new with Julia, and I’m having troubles with my MINLP optimization problem that I used to solve with MATLAB. I can’t find a way to provide an user-defined objective function to the @NLobjective ma…

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## [Nested index for a collection of JuMP variables?](https://discourse.julialang.org/t/nested-index-for-a-collection-of-jump-variables/33504)

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**Author:** [@ccoffrin](https://discourse.julialang.org/u/ccoffrin)\
**Replies:** 2\
**Last updated:** [January 21, 2020, 4:40pm UTC](https://discourse.julialang.org/t/nested-index-for-a-collection-of-jump-variables/33504 "2020-01-21T16:40:09Z")

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I would like to build a two index JuMP variable that can be accessed like x\[i\]\[j\] rather than x\[i,j\] is there a way to acomplish this with the @variable macro?

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## [Recommendations for a Web App for Noob](https://discourse.julialang.org/t/recommendations-for-a-web-app-for-noob/15931)

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**Author:** [@rickhg12hs](https://discourse.julialang.org/u/rickhg12hs)\
**Replies:** 18\
**Last updated:** [January 21, 2020, 1:19pm UTC](https://discourse.julialang.org/t/recommendations-for-a-web-app-for-noob/15931 "2020-01-21T13:19:24Z")

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I’d like to make a very basic WebApp running locally where the user can see some basic text/graphics, select various options, toggles, items from a list, input text, select files, set parameters, etc. Underneath (the gut…

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## [Is there in Julia something similar to min(X, Y) of Matlab where X and Y are matrices of same dimensions](https://discourse.julialang.org/t/is-there-in-julia-something-similar-to-min-x-y-of-matlab-where-x-and-y-are-matrices-of-same-dimensions/33475)

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**Author:** [@Ujku\_KU](https://discourse.julialang.org/u/Ujku_KU)\
**Replies:** 4\
**Last updated:** [January 21, 2020, 6:25am UTC](https://discourse.julialang.org/t/is-there-in-julia-something-similar-to-min-x-y-of-matlab-where-x-and-y-are-matrices-of-same-dimensions/33475 "2020-01-21T06:25:17Z")

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Hi guys, just wondering if there is a function in Julia similar to min(X, Y) (where X and Y are matrices of same dimension) of Matlab. The result is a matrix of the same dimensions as X and Y with elements t…

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## [Passing array of pointers to CUDA kernel](https://discourse.julialang.org/t/passing-array-of-pointers-to-cuda-kernel/33570)

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**Author:** [@Michael\_Benton](https://discourse.julialang.org/u/Michael_Benton)\
**Replies:** 2\
**Last updated:** [January 20, 2020, 5:00pm UTC](https://discourse.julialang.org/t/passing-array-of-pointers-to-cuda-kernel/33570 "2020-01-20T17:00:09Z")

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I need to be able to stack arbitrarily sized cuarrays and CuTextures as a single input to a kernel, so I can do operations in the kernel that loop over the data like so: (get GitHub - cdsousa/CuTextures.jl: \[DEPRECATED,…

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## [Restoration phase failed](https://discourse.julialang.org/t/restoration-phase-failed/33590)

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**Author:** [@GiuliaM](https://discourse.julialang.org/u/GiuliaM)\
**Replies:** 1\
**Last updated:** [January 20, 2020, 3:27pm UTC](https://discourse.julialang.org/t/restoration-phase-failed/33590 "2020-01-20T15:27:48Z")

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Hi everyone! I try to optimize a nonlinear problem with Ipopt (v0.6.1) using JuMP (v0.20.1). When the algorithm terminates, the output message is: “EXIT: Restoration Failed! Restoration phase converged to a feasible …

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## [JuMP nonlinear optimization not converging for camera calibration code](https://discourse.julialang.org/t/jump-nonlinear-optimization-not-converging-for-camera-calibration-code/33565)

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**Author:** [@brianguenter](https://discourse.julialang.org/u/brianguenter)\
**Replies:** 2\
**Last updated:** [January 20, 2020, 3:25pm UTC](https://discourse.julialang.org/t/jump-nonlinear-optimization-not-converging-for-camera-calibration-code/33565 "2020-01-20T15:25:21Z")

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I am using JuMP optimization to compute distortion correction parameters in camera images. This is a first step toward a more complete camera calibration package. It’s the first time I’ve used JuMP and the optimization…

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## [ForwardDiff: How to get the derivative part of a dual number](https://discourse.julialang.org/t/forwarddiff-how-to-get-the-derivative-part-of-a-dual-number/33560)

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**Author:** [@zdenek\_hurak](https://discourse.julialang.org/u/zdenek_hurak)\
**Replies:** 4\
**Last updated:** [January 20, 2020, 10:00am UTC](https://discourse.julialang.org/t/forwarddiff-how-to-get-the-derivative-part-of-a-dual-number/33560 "2020-01-20T10:00:20Z")

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How do I get the derivative part b (or whatever it is called) of a dual number given by a+b\\epsilon, \\quad \\epsilon^2=0, defined using ForwardDiff package? In particular, with the dual number 3+1\\epsilon given by julia\>…

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## [Jupyter notebook: Use pgf code instead of pdf/svg image for export to latex](https://discourse.julialang.org/t/jupyter-notebook-use-pgf-code-instead-of-pdf-svg-image-for-export-to-latex/33344)

<div class="topic-metadata">

**Author:** [@karlroyen](https://discourse.julialang.org/u/karlroyen)\
**Replies:** 11\
**Last updated:** [January 20, 2020, 9:58am UTC](https://discourse.julialang.org/t/jupyter-notebook-use-pgf-code-instead-of-pdf-svg-image-for-export-to-latex/33344 "2020-01-20T09:58:00Z")

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When displaying DataFrames in a Jupyter notebook they are nicely rendered using html. When you export the notebook to latex they are nicely exported as latex code creating that table. Is it possible to have the same fun…

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## [Will the new DataFrames be memory mapped?](https://discourse.julialang.org/t/will-the-new-dataframes-be-memory-mapped/1022)

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**Author:** [@Fred](https://discourse.julialang.org/u/Fred)\
**Replies:** 11\
**Last updated:** [January 20, 2020, 12:05am UTC](https://discourse.julialang.org/t/will-the-new-dataframes-be-memory-mapped/1022 "2020-01-20T00:05:16Z")

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In Julia, large Arrays can be memory mapped using the function Mmap.mmap(type::Type{Array{T, N}}, dims). But I have to work with large DataFrames (I have to keep columns and rows names and often NA values) in geno-trans…

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## [Struggling with parallel code in MCMC simulation](https://discourse.julialang.org/t/struggling-with-parallel-code-in-mcmc-simulation/33448)

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**Author:** [@johnheyer](https://discourse.julialang.org/u/johnheyer)\
**Replies:** 7\
**Last updated:** [January 17, 2020, 7:52pm UTC](https://discourse.julialang.org/t/struggling-with-parallel-code-in-mcmc-simulation/33448 "2020-01-17T19:52:50Z")

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Hi! I’m really struggling with parallel code execution in Julia. I have implemented an MCMC sampler that depends on packages such as Distributions, Random, etc., as well as two other julia files which I have written. T…

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## [Julia Linear System Solver (\`mldivide()\`)](https://discourse.julialang.org/t/julia-linear-system-solver-mldivide/33447)

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**Author:** [@RoyiAvital](https://discourse.julialang.org/u/RoyiAvital)\
**Replies:** 6\
**Last updated:** [January 17, 2020, 12:37pm UTC](https://discourse.julialang.org/t/julia-linear-system-solver-mldivide/33447 "2020-01-17T12:37:19Z")

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In the question Solution of Underdetermined Systems Using LAPACK @stevengj mentioned that the \\ operator in Julia returns the Minimum Norm Solution for Under determined System. The Matrix Division operator, \\ according…

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## [How to redraw a subplot instead of overlaying, GR](https://discourse.julialang.org/t/how-to-redraw-a-subplot-instead-of-overlaying-gr/18473)

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**Author:** [@Donut\_Meepo](https://discourse.julialang.org/u/Donut_Meepo)\
**Replies:** 3\
**Last updated:** [January 16, 2020, 4:55pm UTC](https://discourse.julialang.org/t/how-to-redraw-a-subplot-instead-of-overlaying-gr/18473 "2020-01-16T16:55:39Z")

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Hi, I am trying to fill the subplots of a layout using GR backend layout = @layout \[grid(1,2); grid(1,2); grid(1,1)\]; plot(layout=layout) #draw at position2 plot!(1:10, rand(10), subplot=2) #want to redraw instead of o…

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## [Finite element mesh interface](https://discourse.julialang.org/t/finite-element-mesh-interface/33325)

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**Author:** [@juliohm](https://discourse.julialang.org/u/juliohm)\
**Replies:** 19\
**Last updated:** [January 16, 2020, 8:51am UTC](https://discourse.julialang.org/t/finite-element-mesh-interface/33325 "2020-01-16T08:51:24Z")

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Dear all, Do you know a paper, book or any published material that attempts to define an interface for general finite element meshes? I am in the process of finalizing a proposal interface, and would like to share it w…

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## [Problem with Mosek](https://discourse.julialang.org/t/problem-with-mosek/33427)

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**Author:** [@Shuvomoy\_Das\_Gupta](https://discourse.julialang.org/u/Shuvomoy_Das_Gupta)\
**Replies:** 4\
**Last updated:** [January 16, 2020, 1:51am UTC](https://discourse.julialang.org/t/problem-with-mosek/33427 "2020-01-16T01:51:29Z")

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Dear All, I am trying to solve an SDP using Convex.jl and Mosek. My Mosek version is 9.1.11, and Convex.jl version is 0.12.6. My Julia version is 1.3. I have installed Mosek with an academic license, and it seems to be …

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## [GR.jl: Change backgroundcolor of savefig() image](https://discourse.julialang.org/t/gr-jl-change-backgroundcolor-of-savefig-image/33382)

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**Author:** [@al314](https://discourse.julialang.org/u/al314)\
**Replies:** 2\
**Last updated:** [January 15, 2020, 10:25am UTC](https://discourse.julialang.org/t/gr-jl-change-backgroundcolor-of-savefig-image/33382 "2020-01-15T10:25:20Z")

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Hi all, The script using GR plot(randn(199)) savefig("./test.PNG") produces a PNG picture with a transparent background. How to fix this and make it for example white? Thanks.

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