# General Usage

**URL:** https://discourse.julialang.org/c/usage/6.md?page=737

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**Page:** 738

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## [How can I return the number of missings / uniques of a numerical type column?](https://discourse.julialang.org/t/how-can-i-return-the-number-of-missings-uniques-of-a-numerical-type-column/41726)

<div class="topic-metadata">

**Author:** [@Julia1](https://discourse.julialang.org/u/Julia1)\
**Replies:** 4\
**Last updated:** [June 19, 2020, 2:56pm UTC](https://discourse.julialang.org/t/how-can-i-return-the-number-of-missings-uniques-of-a-numerical-type-column/41726 "2020-06-19T14:56:17Z")

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Hi how’s it going? I’m trying to filter columns based on number of unique values and number of missings, and I just noticed that when calling the Describe() method on a DataFrame, it doesn’t work for numerical columns. …

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## [Cross-platform unpacking of rar archive?](https://discourse.julialang.org/t/cross-platform-unpacking-of-rar-archive/41717)

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**Author:** [@jbrea](https://discourse.julialang.org/u/jbrea)\
**Replies:** 5\
**Last updated:** [June 19, 2020, 1:35pm UTC](https://discourse.julialang.org/t/cross-platform-unpacking-of-rar-archive/41717 "2020-06-19T13:35:45Z")

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Is there are a cross-platform way to unpack rar archives in julia? I saw there is the unregistered LibArchive.jl, but I got build errors in julia 1.4.1. Is there an alternative? EDIT: I found p7zip\_jll in the meantime. …

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## [Getting a reference to, and not a copy of, a field value](https://discourse.julialang.org/t/getting-a-reference-to-and-not-a-copy-of-a-field-value/9042)

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**Author:** [@ablaom](https://discourse.julialang.org/u/ablaom)\
**Replies:** 12\
**Last updated:** [June 19, 2020, 1:08pm UTC](https://discourse.julialang.org/t/getting-a-reference-to-and-not-a-copy-of-a-field-value/9042 "2020-06-19T13:08:40Z")

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The code y = object.x binds a copy of object.x to y. How do I make bind y to object.x itself? The reason for my question is this: To improve readability, I want to do something like this: function foo(cache) X = c…

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## [Using BlackBoxOptim with Flux](https://discourse.julialang.org/t/using-blackboxoptim-with-flux/41724)

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**Author:** [@compleat](https://discourse.julialang.org/u/compleat)\
**Replies:** 0\
**Last updated:** [June 19, 2020, 1:00pm UTC](https://discourse.julialang.org/t/using-blackboxoptim-with-flux/41724 "2020-06-19T13:00:18Z")

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It has been noted that BlackBoxOptim now may be used as one of the optimizers in Flux in the latest release, but I can’t find any documentation or examples for how to use it. I know how to use each separately. I saw …

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## [How to Plots.plot a GroupedDataFrame?](https://discourse.julialang.org/t/how-to-plots-plot-a-groupeddataframe/41723)

<div class="topic-metadata">

**Author:** [@gedankenexperiment](https://discourse.julialang.org/u/gedankenexperiment)\
**Replies:** 1\
**Last updated:** [June 19, 2020, 12:28pm UTC](https://discourse.julialang.org/t/how-to-plots-plot-a-groupeddataframe/41723 "2020-06-19T12:28:46Z")

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Hi there, I recently asked a question on how to do grouping in Julia Plots, the answer was to encapsulate a mapping and feed the function to the group keyword in the plot function. But learning more about DataFrames, I…

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## [Broadcasting \*= and the like](https://discourse.julialang.org/t/broadcasting-and-the-like/41702)

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**Author:** [@binarygcd](https://discourse.julialang.org/u/binarygcd)\
**Replies:** 3\
**Last updated:** [June 19, 2020, 6:54am UTC](https://discourse.julialang.org/t/broadcasting-and-the-like/41702 "2020-06-19T06:54:07Z")

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I tried using broadcast for computing the radicals of integers 1 to limit. But it was significantly slower than the for loop version. Am I doing something wrong? I tried map! but I’m not sure if I got it right so please …

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## [Providing precompiled ji files within a package](https://discourse.julialang.org/t/providing-precompiled-ji-files-within-a-package/41709)

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**Author:** [@Azzaare](https://discourse.julialang.org/u/Azzaare)\
**Replies:** 4\
**Last updated:** [June 19, 2020, 6:22am UTC](https://discourse.julialang.org/t/providing-precompiled-ji-files-within-a-package/41709 "2020-06-19T06:22:27Z")

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Hi! I am developing a package with a heavy precompilation time (5-10 minutes, but could be a bit more). The .ji are not that big though and it runs pretty fast. Is it possible to provide .ji files (per platform I suppo…

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## [Is this a legal use of Zip?](https://discourse.julialang.org/t/is-this-a-legal-use-of-zip/41703)

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**Author:** [@PetrKryslUCSD](https://discourse.julialang.org/u/PetrKryslUCSD)\
**Replies:** 2\
**Last updated:** [June 19, 2020, 2:52am UTC](https://discourse.julialang.org/t/is-this-a-legal-use-of-zip/41703 "2020-06-19T02:52:50Z")

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I would like to create a collection of iterators. Before I start iterating I would like to access individual iterators. Doing that requires accessing the field of Zip. Does this look okay? N = 3 it1 = fill(1, N) it2 = f…

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## [Any way to reduce/change number of threads (for the Benchmark Game)](https://discourse.julialang.org/t/any-way-to-reduce-change-number-of-threads-for-the-benchmark-game/41706)

<div class="topic-metadata">

**Author:** [@Palli](https://discourse.julialang.org/u/Palli)\
**Replies:** 0\
**Last updated:** [June 19, 2020, 1:21am UTC](https://discourse.julialang.org/t/any-way-to-reduce-change-number-of-threads-for-the-benchmark-game/41706 "2020-06-19T01:21:55Z")

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A. Using 4 threads adds 20.3 ms (37 on average, but I trust the minimum better) to startup (would there be a way for Julia do delay adding them until the threads actually used?). The obvious solution is not asking for …

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## [Read multiple DataFrames stored in a single text file](https://discourse.julialang.org/t/read-multiple-dataframes-stored-in-a-single-text-file/41673)

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**Author:** [@evad](https://discourse.julialang.org/u/evad)\
**Replies:** 8\
**Last updated:** [June 19, 2020, 1:19am UTC](https://discourse.julialang.org/t/read-multiple-dataframes-stored-in-a-single-text-file/41673 "2020-06-19T01:19:33Z")

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I have a text file with multiple DataFrames in the following format (tab separated): %T table1 %F col1 col2 col3 %R 1 2 3 %T table2 %F col1 col2 col3 col4 %R 1 2 3 4 %R 5 6 …

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## [OpenBLAS is faster than Intel MKL on AMD Hardware (Ryzen)](https://discourse.julialang.org/t/openblas-is-faster-than-intel-mkl-on-amd-hardware-ryzen/8033)

<div class="topic-metadata">

**Author:** [@Elrod](https://discourse.julialang.org/u/Elrod)\
**Replies:** 40\
**Last updated:** [June 19, 2020, 1:03am UTC](https://discourse.julialang.org/t/openblas-is-faster-than-intel-mkl-on-amd-hardware-ryzen/8033 "2020-06-19T01:03:05Z")

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Questions about MKL vs OpenBLAS come up a lot, for example in comparisons with Matlab (linked to MKL), and a lot of users have issues building with MKL, eg here. Of course, one can easily download an MKL binary with Juli…

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## [ODE solver save intermediate outputs (y = C\*x + D\*u)](https://discourse.julialang.org/t/ode-solver-save-intermediate-outputs-y-c-x-d-u/41697)

<div class="topic-metadata">

**Author:** [@mopg](https://discourse.julialang.org/u/mopg)\
**Replies:** 5\
**Last updated:** [June 19, 2020, 12:38am UTC](https://discourse.julialang.org/t/ode-solver-save-intermediate-outputs-y-c-x-d-u/41697 "2020-06-19T00:38:04Z")

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I am using DifferentialEquations.jl for solving an ODE, and it works great. However, I’d like to save intermediate outputs, and I can’t figure out how to do that. Consider the example below: using DifferentialEquations…

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## [Inlining and function boundaries](https://discourse.julialang.org/t/inlining-and-function-boundaries/41686)

<div class="topic-metadata">

**Author:** [@Kiuhnm\_Mnhuik](https://discourse.julialang.org/u/Kiuhnm_Mnhuik)\
**Replies:** 1\
**Last updated:** [June 18, 2020, 7:45pm UTC](https://discourse.julialang.org/t/inlining-and-function-boundaries/41686 "2020-06-18T19:45:42Z")

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I read that inlining, by removing function boundaries, may cause type instability. Is this true? This doesn’t seem too hard to fix, but I’m not familiar with Julia internals.

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## [Testing private package fails based on dependency](https://discourse.julialang.org/t/testing-private-package-fails-based-on-dependency/41619)

<div class="topic-metadata">

**Author:** [@doomphoenix-qxz](https://discourse.julialang.org/u/doomphoenix-qxz)\
**Replies:** 8\
**Last updated:** [June 18, 2020, 6:39pm UTC](https://discourse.julialang.org/t/testing-private-package-fails-based-on-dependency/41619 "2020-06-18T18:39:42Z")

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I have a private package that I am trying to test. When I run the test suite, it fails, claiming it can’t find CSV: ERROR: LoadError: ArgumentError: Package CSV not found in current path: - Run \`import Pkg; Pkg.add("CSV…

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## [Help speedup a tight triple loop](https://discourse.julialang.org/t/help-speedup-a-tight-triple-loop/41648)

<div class="topic-metadata">

**Author:** [@biona001](https://discourse.julialang.org/u/biona001)\
**Replies:** 7\
**Last updated:** [June 18, 2020, 6:15pm UTC](https://discourse.julialang.org/t/help-speedup-a-tight-triple-loop/41648 "2020-06-18T18:15:44Z")

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Hello Julia, The following code is inside a multithreaded loop which gets called a lot. It essentially loops over a symmetric matrix M (dimension ~50k at most) and computes the minimum with respect to each row of N in a…

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## [Array of Plot objects](https://discourse.julialang.org/t/array-of-plot-objects/41679)

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**Author:** [@jmurray](https://discourse.julialang.org/u/jmurray)\
**Replies:** 11\
**Last updated:** [June 18, 2020, 6:13pm UTC](https://discourse.julialang.org/t/array-of-plot-objects/41679 "2020-06-18T18:13:23Z")

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I want to make an array containing plots, but the two approaches I’ve tried both fail. My first approach was to allocate an empty array and push! new plot objects: p\_arr1 = Array{Plots.Plot{Plots.GRBackend},1}\[\] push!(…

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## [Issue with include](https://discourse.julialang.org/t/issue-with-include/41676)

<div class="topic-metadata">

**Author:** [@mkphys](https://discourse.julialang.org/u/mkphys)\
**Replies:** 4\
**Last updated:** [June 18, 2020, 4:36pm UTC](https://discourse.julialang.org/t/issue-with-include/41676 "2020-06-18T16:36:44Z")

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I am seeing an odd issue with how include works. I am using Julia 1.0.2. Here is the simplest case that seems to cause issues: julia\_include\_issue.jl function f1() println("In f1()") include("params.jl") pri…

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## [Mapreduce with function that has multiple return values](https://discourse.julialang.org/t/mapreduce-with-function-that-has-multiple-return-values/41674)

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**Author:** [@jebej](https://discourse.julialang.org/u/jebej)\
**Replies:** 2\
**Last updated:** [June 18, 2020, 4:22pm UTC](https://discourse.julialang.org/t/mapreduce-with-function-that-has-multiple-return-values/41674 "2020-06-18T16:22:38Z")

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I frequently run into an issue where I want to apply a function over a range of inputs and combine the output into arrays, where the function returns more than 1 value, and each return value should be collected in a diff…

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## [Couldn't process recipe args: (Array{Float64,2}, Array{Float64,2}, Array{Float64,2}, Array{Float64,2})](https://discourse.julialang.org/t/couldnt-process-recipe-args-array-float64-2-array-float64-2-array-float64-2-array-float64-2/41672)

<div class="topic-metadata">

**Author:** [@hafez\_ahmad](https://discourse.julialang.org/u/hafez_ahmad)\
**Replies:** 1\
**Last updated:** [June 18, 2020, 3:41pm UTC](https://discourse.julialang.org/t/couldnt-process-recipe-args-array-float64-2-array-float64-2-array-float64-2-array-float64-2/41672 "2020-06-18T15:41:13Z")

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I am trying to learn Channel Flow with Navier-Stokes from this link Welcome to CFD Julia. I am getting error . nx = 41; ny = 41; nt = 500; nit=50; c = 1; dx = 2/(nx-1); dy = 2/(ny-1); x=range(0, stop=2, length…

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## [Testing package where the test depends on local dev'ed package fails in Julia 1.4.2 with ERROR: can not merge projects](https://discourse.julialang.org/t/testing-package-where-the-test-depends-on-local-deved-package-fails-in-julia-1-4-2-with-error-can-not-merge-projects/41611)

<div class="topic-metadata">

**Author:** [@alkoedl](https://discourse.julialang.org/u/alkoedl)\
**Replies:** 3\
**Last updated:** [June 18, 2020, 2:30pm UTC](https://discourse.julialang.org/t/testing-package-where-the-test-depends-on-local-deved-package-fails-in-julia-1-4-2-with-error-can-not-merge-projects/41611 "2020-06-18T14:30:38Z")

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I have a package (say AAA) where the package itself and the tests depend on a local dev’ed package (BBB). Accordingly, I have package BBB both in AAA’s environment and in AAA/test environment like this: Project AAA v0.1…

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## [Completely eliminating any inference for certain functions](https://discourse.julialang.org/t/completely-eliminating-any-inference-for-certain-functions/41582)

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**Author:** [@jules](https://discourse.julialang.org/u/jules)\
**Replies:** 6\
**Last updated:** [June 18, 2020, 2:00pm UTC](https://discourse.julialang.org/t/completely-eliminating-any-inference-for-certain-functions/41582 "2020-06-18T14:00:26Z")

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Is there a way to completely skip internal type inference for functions? If I have tons of high-level API functions in a package and only a couple of performance-critical functions, I would like the top part to be like …

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## [CSV.jl: Write csv row by row](https://discourse.julialang.org/t/csv-jl-write-csv-row-by-row/41593)

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**Author:** [@altre](https://discourse.julialang.org/u/altre)\
**Replies:** 3\
**Last updated:** [June 18, 2020, 1:52pm UTC](https://discourse.julialang.org/t/csv-jl-write-csv-row-by-row/41593 "2020-06-18T13:52:38Z")

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I have an application which writes a csv as an output but never holds the complete csv in memory. I would like to use a library such as CSV.jl to a) take advantage of optimizations (CSV.jl is super fast for reading!) …

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## [Calculate Hessian after providing gradient: NLSolversBase, Optim](https://discourse.julialang.org/t/calculate-hessian-after-providing-gradient-nlsolversbase-optim/41629)

<div class="topic-metadata">

**Author:** [@marinooss](https://discourse.julialang.org/u/marinooss)\
**Replies:** 0\
**Last updated:** [June 17, 2020, 8:48pm UTC](https://discourse.julialang.org/t/calculate-hessian-after-providing-gradient-nlsolversbase-optim/41629 "2020-06-17T20:48:53Z")

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I am using the following special interface from NLSolversBase, to minimize a function. function fg!(F, G, x) common\_calc(…) if !(G == nothing) # mutating calculations specific to g! end if !(F …

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## [3D line plot of the elements of 3 vectors](https://discourse.julialang.org/t/3d-line-plot-of-the-elements-of-3-vectors/41662)

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**Author:** [@fusion809](https://discourse.julialang.org/u/fusion809)\
**Replies:** 2\
**Last updated:** [June 18, 2020, 12:29pm UTC](https://discourse.julialang.org/t/3d-line-plot-of-the-elements-of-3-vectors/41662 "2020-06-18T12:29:38Z")

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I’d like to generate a 3D line plot using data in three vectors labelled x, y and z. I’ve tried using PyPlot’s plot3D and I received the error: PyError ($(Expr(:escape, :(ccall(#= /home/fusion809/.julia/packages/PyCall/…

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## [Parrallel programming](https://discourse.julialang.org/t/parrallel-programming/41659)

<div class="topic-metadata">

**Author:** [@hyacykcharel](https://discourse.julialang.org/u/hyacykcharel)\
**Replies:** 1\
**Last updated:** [June 18, 2020, 11:04am UTC](https://discourse.julialang.org/t/parrallel-programming/41659 "2020-06-18T11:04:04Z")

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hello im trying to to a parallel compuing but it is not workig can someone please correct this code for me thans? using Distributed addprocs(1) nprocs() procs() workers() nworkers() @everywhere using Distri…

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## [Can I build webpages and especially dashboards in Julia](https://discourse.julialang.org/t/can-i-build-webpages-and-especially-dashboards-in-julia/10913)

<div class="topic-metadata">

**Author:** [@vikram-rawat](https://discourse.julialang.org/u/vikram-rawat)\
**Replies:** 19\
**Last updated:** [August 3, 2019, 9:05pm UTC](https://discourse.julialang.org/t/can-i-build-webpages-and-especially-dashboards-in-julia/10913 "2019-08-03T21:05:47Z")

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I have no prior knowledge of the language yet I have heard a lot of good things about the language. but before I want to start it I want to know can I build web pages and dashboards in Julia. If so what library should I…

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## [I can't start a Jupyter notebook from the Julia terminal](https://discourse.julialang.org/t/i-cant-start-a-jupyter-notebook-from-the-julia-terminal/4649)

<div class="topic-metadata">

**Author:** [@Jean-Victor](https://discourse.julialang.org/u/Jean-Victor)\
**Replies:** 6\
**Last updated:** [June 18, 2020, 5:24am UTC](https://discourse.julialang.org/t/i-cant-start-a-jupyter-notebook-from-the-julia-terminal/4649 "2020-06-18T05:24:02Z")

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All I get is the following message → Process(setenv(jupyter notebook --NotebookApp.iopub\_data\_rate\_limit=2147483647; dir=“/home/jean-victor”), ProcessExited(1))

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## [Solving heat diffusion PDE using DiffEqTools.jl and DifferentialEquations.jl](https://discourse.julialang.org/t/solving-heat-diffusion-pde-using-diffeqtools-jl-and-differentialequations-jl/41630)

<div class="topic-metadata">

**Author:** [@g4lvanix](https://discourse.julialang.org/u/g4lvanix)\
**Replies:** 2\
**Last updated:** [June 18, 2020, 5:20am UTC](https://discourse.julialang.org/t/solving-heat-diffusion-pde-using-diffeqtools-jl-and-differentialequations-jl/41630 "2020-06-18T05:20:00Z")

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Hi, I saw a great talk by Chris Rackauckas from JuliaCon 2018 on how to solve PDEs using Julia and decided to give it a whirl. The problem I’m trying to solve is the diffusion equation: Find u(t,x) such that u\_t = alph…

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## [FORTRAN STOP leads to exiting Julia REPL](https://discourse.julialang.org/t/fortran-stop-leads-to-exiting-julia-repl/41643)

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**Author:** [@mopg](https://discourse.julialang.org/u/mopg)\
**Replies:** 2\
**Last updated:** [June 18, 2020, 3:36am UTC](https://discourse.julialang.org/t/fortran-stop-leads-to-exiting-julia-repl/41643 "2020-06-18T03:36:23Z")

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I am wrapping a FORTRAN library that has a bunch of STOP commands in it (to throw errors). However, when I call the library from Julia and one of those errors is reached, the whole process exits (including the Julia REPL…

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## [Do comprehensions implicitly use sizehint?](https://discourse.julialang.org/t/do-comprehensions-implicitly-use-sizehint/41452)

<div class="topic-metadata">

**Author:** [@nacnudus](https://discourse.julialang.org/u/nacnudus)\
**Replies:** 3\
**Last updated:** [June 17, 2020, 9:33pm UTC](https://discourse.julialang.org/t/do-comprehensions-implicitly-use-sizehint/41452 "2020-06-17T21:33:35Z")

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The Wikibook on creating dictionaries gives an example that uses a comprehension. Would Julia automatically use a sizehint based on the size of for i = 0:5:360? Or would it be better to do that explicitly by creating a…

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