# Latest

**URL:** https://discourse.julialang.org/latest.md?page=1691

[Latest](https://discourse.julialang.org/latest.md) · [Categories](https://discourse.julialang.org/categories.md) · [Tags](https://discourse.julialang.org/tags.md)

**Page:** 1692

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## [Selecting the value in a particular row of a column in a DataFrame](https://discourse.julialang.org/t/selecting-the-value-in-a-particular-row-of-a-column-in-a-dataframe/42961)

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**Author:** [@Nash](https://discourse.julialang.org/u/Nash)\
**Replies:** 1\
**Last updated:** [July 12, 2020, 9:02pm UTC](https://discourse.julialang.org/t/selecting-the-value-in-a-particular-row-of-a-column-in-a-dataframe/42961 "2020-07-12T21:02:13Z")

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The following selects an entire column in a DataFrame: select(df,:x) But how do I select the second row of x, say?

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## [How we can write quadratic equation (Mathematical functions) In Julia](https://discourse.julialang.org/t/how-we-can-write-quadratic-equation-mathematical-functions-in-julia/37409)

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**Author:** [@Neeraj\_Verma\_ASETRAI](https://discourse.julialang.org/u/Neeraj_Verma_ASETRAI)\
**Replies:** 3\
**Last updated:** [April 14, 2020, 10:17pm UTC](https://discourse.julialang.org/t/how-we-can-write-quadratic-equation-mathematical-functions-in-julia/37409 "2020-04-14T22:17:06Z")

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Suppose i wanted to write a fun y = x^2+1 and wanted to plot in scatter. So how can i plot this in Julia? i tried this method but didn’t work y(x) = x^2+1 x = 1:10 scatter(x,y(x))

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## [Philosophical discussion of Elif, Elsif, ElseIf](https://discourse.julialang.org/t/philosophical-discussion-of-elif-elsif-elseif/42885)

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**Author:** [@Bryan\_So](https://discourse.julialang.org/u/Bryan_So)\
**Replies:** 3\
**Last updated:** [July 12, 2020, 7:10pm UTC](https://discourse.julialang.org/t/philosophical-discussion-of-elif-elsif-elseif/42885 "2020-07-12T19:10:36Z")

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Most languages define ElseIf as a keyword. It makes no sense to me. Julia: if \<condition\> ... elseif \<condition\> ... else ... end Python: if \<condition\>: ... elif \<condition\>: ... else: ... e…

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## [Status of question mark syntax for missing values](https://discourse.julialang.org/t/status-of-question-mark-syntax-for-missing-values/27189)

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**Author:** [@juliohm](https://discourse.julialang.org/u/juliohm)\
**Replies:** 6\
**Last updated:** [July 12, 2020, 7:07pm UTC](https://discourse.julialang.org/t/status-of-question-mark-syntax-for-missing-values/27189 "2020-07-12T19:07:11Z")

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I remember seeing a discussion somewhere about using the syntax T? to mean Union{T,Missing}. What was the outcome of this discussion? I personally find the syntax very clever, and it would help clean up a lot of code whe…

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## [Example of nonlinear optimization with Ipopt](https://discourse.julialang.org/t/example-of-nonlinear-optimization-with-ipopt/42954)

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**Author:** [@mayar](https://discourse.julialang.org/u/mayar)\
**Replies:** 3\
**Last updated:** [July 12, 2020, 6:55pm UTC](https://discourse.julialang.org/t/example-of-nonlinear-optimization-with-ipopt/42954 "2020-07-12T18:55:41Z")

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hello can you provide me with an example or link to an example on NL optimization with Ipopt Thank you

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## [Using DiffEq isoutofdomain to enforce positivity](https://discourse.julialang.org/t/using-diffeq-isoutofdomain-to-enforce-positivity/42443)

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**Author:** [@emily\_dj](https://discourse.julialang.org/u/emily_dj)\
**Replies:** 13\
**Last updated:** [July 12, 2020, 6:24pm UTC](https://discourse.julialang.org/t/using-diffeq-isoutofdomain-to-enforce-positivity/42443 "2020-07-12T18:24:11Z")

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I’m trying to enforce positivity of my solution using the isoutofdomain solver option in the DifferentialEquations package, yet it seems that an error within my derivative function (which requires positivity at the time …

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## [Abnormally exit after executed a very simple expression](https://discourse.julialang.org/t/abnormally-exit-after-executed-a-very-simple-expression/42930)

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**Author:** [@astrojhgu](https://discourse.julialang.org/u/astrojhgu)\
**Replies:** 4\
**Last updated:** [July 12, 2020, 3:47pm UTC](https://discourse.julialang.org/t/abnormally-exit-after-executed-a-very-simple-expression/42930 "2020-07-12T15:47:56Z")

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Update: After ugrade to 1.4.2 this error disappears. Following is the original post, which happens under 1.4.1 I’m using Julia 1.4.1 inside a singularity+ubuntu20.04 container Most of the behaviours are normal, but If I…

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## [Exporting to pdf with GR results in font size 1.5 larger](https://discourse.julialang.org/t/exporting-to-pdf-with-gr-results-in-font-size-1-5-larger/42953)

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**Author:** [@yanivab](https://discourse.julialang.org/u/yanivab)\
**Replies:** 0\
**Last updated:** [July 12, 2020, 3:41pm UTC](https://discourse.julialang.org/t/exporting-to-pdf-with-gr-results-in-font-size-1-5-larger/42953 "2020-07-12T15:41:59Z")

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Hello, I’m using Plots.jl with GR for plotting, and trying to export my figures to pdf. I set font size using the theme command: theme(:default, xguidefontsize=9, yguidefontsize=9, xtickfontsize=7, ytickfontsize=7, …

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## [Given a Julia function \`f\` and its arguments \`agrs\` return typed Julia source code via a macro](https://discourse.julialang.org/t/given-a-julia-function-f-and-its-arguments-agrs-return-typed-julia-source-code-via-a-macro/42947)

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**Author:** [@Impressium](https://discourse.julialang.org/u/Impressium)\
**Replies:** 15\
**Last updated:** [July 12, 2020, 3:20pm UTC](https://discourse.julialang.org/t/given-a-julia-function-f-and-its-arguments-agrs-return-typed-julia-source-code-via-a-macro/42947 "2020-07-12T15:20:54Z")

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Is there a macro for that? Or is it possible to write one? It’s always easier to understand via an example: function f(x,y) a = sqrt(x) b = x\*y return a + b end Macro call: @get\_typed\_source\_code f(1,2) f…

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## [Installing PyCall](https://discourse.julialang.org/t/installing-pycall/42952)

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**Author:** [@marouane1994](https://discourse.julialang.org/u/marouane1994)\
**Replies:** 0\
**Last updated:** [July 12, 2020, 3:10pm UTC](https://discourse.julialang.org/t/installing-pycall/42952 "2020-07-12T15:10:37Z")

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For some reason the build of PyCall takes forever on my PC and the reason is unknown, it stops at Building PyCall → C:\\Users\\Administrator.julia\\packages\\PyCall\\zqDXB\\deps\\build.log\` any idea why it’s taking forever to …

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## [Assembling data using DataFrame such that rows where a particular array has empty elements are discounted](https://discourse.julialang.org/t/assembling-data-using-dataframe-such-that-rows-where-a-particular-array-has-empty-elements-are-discounted/42946)

<div class="topic-metadata">

**Author:** [@Nash](https://discourse.julialang.org/u/Nash)\
**Replies:** 5\
**Last updated:** [July 12, 2020, 2:33pm UTC](https://discourse.julialang.org/t/assembling-data-using-dataframe-such-that-rows-where-a-particular-array-has-empty-elements-are-discounted/42946 "2020-07-12T14:33:00Z")

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I am collecting arrays of data using DataFrames: df = DataFrame(marketIds = x\[:,1\], stockIds = x\[:,2\], price = x\[:,3\]) In the array of prices, some elements are empty. How do I assemble df such that rows where price is…

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## [Why does Core.Compiler.return\_type expect function instance instead of function type?](https://discourse.julialang.org/t/why-does-core-compiler-return-type-expect-function-instance-instead-of-function-type/42521)

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**Author:** [@schlichtanders](https://discourse.julialang.org/u/schlichtanders)\
**Replies:** 11\
**Last updated:** [July 12, 2020, 2:29pm UTC](https://discourse.julialang.org/t/why-does-core-compiler-return-type-expect-function-instance-instead-of-function-type/42521 "2020-07-12T14:29:28Z")

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While Core.Compiler.return\_type can give imprecise results, it is quite handy from time to time. Today my question is not about its usage, however about why the first argument - the function - is different compared to th…

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## [What are the functions defined inside other functions called?](https://discourse.julialang.org/t/what-are-the-functions-defined-inside-other-functions-called/42915)

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**Author:** [@PetrKryslUCSD](https://discourse.julialang.org/u/PetrKryslUCSD)\
**Replies:** 6\
**Last updated:** [July 12, 2020, 1:40pm UTC](https://discourse.julialang.org/t/what-are-the-functions-defined-inside-other-functions-called/42915 "2020-07-12T13:40:41Z")

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I’ve been looking for “nested” or “inner” or “subfunction” in the manual: no hits. Does anyone remember?

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## [ImageChipper.jl and ObjectDetectionStats.jl (+ LockandKeyLookups.jl)](https://discourse.julialang.org/t/imagechipper-jl-and-objectdetectionstats-jl-lockandkeylookups-jl/42940)

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**Author:** [@anon92994695](https://discourse.julialang.org/u/anon92994695)\
**Replies:** 0\
**Last updated:** [July 12, 2020, 1:05pm UTC](https://discourse.julialang.org/t/imagechipper-jl-and-objectdetectionstats-jl-lockandkeylookups-jl/42940 "2020-07-12T13:05:29Z")

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Hi everyone, I’m here to announce three packages I’ve made at their early stages related to computer vision and improving Julia’s machine learning ecosystem. ImageChipper.jl - How much image would an image chipper chip…

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## [Simple kernel not working](https://discourse.julialang.org/t/simple-kernel-not-working/42831)

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**Author:** [@Ferran\_Mazzanti](https://discourse.julialang.org/u/Ferran_Mazzanti)\
**Replies:** 10\
**Last updated:** [July 12, 2020, 12:20pm UTC](https://discourse.julialang.org/t/simple-kernel-not-working/42831 "2020-07-12T12:20:14Z")

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Hi again guys :slight\_smile: this time I’m facing one problem that makes me think that I’m missing something very important in CUDA programming, so maybe somebody can help me out to understand what goes on. Consider thi…

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## [What does \`|\>\` mean?](https://discourse.julialang.org/t/what-does-mean/42880)

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**Author:** [@Gus\_Hart](https://discourse.julialang.org/u/Gus_Hart)\
**Replies:** 12\
**Last updated:** [July 12, 2020, 11:59am UTC](https://discourse.julialang.org/t/what-does-mean/42880 "2020-07-12T11:59:29Z")

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I saw this syntax during a Juliacon2018 video that I was watching. It was unfamiliar to me, so I tried to find it in the documentation, but the search functionality didn’t send me anywhere useful. I scrolled through diff…

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## [Get\_color\_palette not found](https://discourse.julialang.org/t/get-color-palette-not-found/42900)

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**Author:** [@erlebach](https://discourse.julialang.org/u/erlebach)\
**Replies:** 11\
**Last updated:** [July 12, 2020, 10:35am UTC](https://discourse.julialang.org/t/get-color-palette-not-found/42900 "2020-07-12T10:35:19Z")

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I am getting a get\_color\_palette undefined in the Plots module after an update. Here is the update: (@v1.4) pkg\> update Plots Updating registry at \`~/.julia/registries/General\` Updating git-repo \`https://github.c…

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## [Write\_parquet with non-standard types](https://discourse.julialang.org/t/write-parquet-with-non-standard-types/42881)

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**Author:** [@freeman](https://discourse.julialang.org/u/freeman)\
**Replies:** 2\
**Last updated:** [July 12, 2020, 9:44am UTC](https://discourse.julialang.org/t/write-parquet-with-non-standard-types/42881 "2020-07-12T09:44:39Z")

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Suppose I have a vector of MyStruct, the fields of which are all “simple” Julia types, and I want to save it to a parquet file. struct MyStruct a::Float64 b::Float64 end x = \[MyStruct(x,y) for (x,y) in zip(rand…

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## [Why is splatting a non-iteratable allowed?](https://discourse.julialang.org/t/why-is-splatting-a-non-iteratable-allowed/42818)

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**Author:** [@Samuel\_Ainsworth](https://discourse.julialang.org/u/Samuel_Ainsworth)\
**Replies:** 30\
**Last updated:** [July 12, 2020, 6:34am UTC](https://discourse.julialang.org/t/why-is-splatting-a-non-iteratable-allowed/42818 "2020-07-12T06:34:06Z")

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Why is this allowed? julia\> \[1.0..., 2.0, 3.0\] 3-element Array{Float64,1}: 1.0 2.0 3.0 It strikes me as non-intuitive, and has already caused me some bugs. It’s especially weird when you think about it relative to …

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## [Spetrum method and DifferentialEquaitons](https://discourse.julialang.org/t/spetrum-method-and-differentialequaitons/42919)

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**Author:** [@hzgzh](https://discourse.julialang.org/u/hzgzh)\
**Replies:** 2\
**Last updated:** [July 12, 2020, 6:29am UTC](https://discourse.julialang.org/t/spetrum-method-and-differentialequaitons/42919 "2020-07-12T06:29:51Z")

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Hi, I use Differentialequantions to solve the pde, \\left\\{\\begin{array}{l} \\frac{\\partial u}{\\partial t}=\\varepsilon \\frac{\\partial^{2} u}{\\partial x^{2}}+u-u^{3}, \\quad-1\<x\<1 \\\\ \\left.u\\right|\_{x=\\pm 1}=\\pm 1 \\\\ \\lef…

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## [Include new test Project file logic also into 1.0?](https://discourse.julialang.org/t/include-new-test-project-file-logic-also-into-1-0/42896)

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**Author:** [@schlichtanders](https://discourse.julialang.org/u/schlichtanders)\
**Replies:** 3\
**Last updated:** [July 12, 2020, 6:24am UTC](https://discourse.julialang.org/t/include-new-test-project-file-logic-also-into-1-0/42896 "2020-07-12T06:24:38Z")

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Hi, I just stumbled upon the switch in the recommendation about where to configure test dependencies. https://julialang.github.io/Pkg.jl/v1/creating-packages/#Test-specific-dependencies-in-Julia-1.2-and-above-1 Apparen…

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## [What parts of .julia can be read-only?](https://discourse.julialang.org/t/what-parts-of-julia-can-be-read-only/42922)

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**Author:** [@denizyuret](https://discourse.julialang.org/u/denizyuret)\
**Replies:** 0\
**Last updated:** [July 12, 2020, 5:18am UTC](https://discourse.julialang.org/t/what-parts-of-julia-can-be-read-only/42922 "2020-07-12T05:18:42Z")

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I am trying to setup a read-only central Julia repository in our GPU cluster using JULIA\_DEPOT\_PATH. However I keep getting errors with certain operations on client machines. As I get errors I symlink directories such as…

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## [Julia 1.2 in Nextjournal](https://discourse.julialang.org/t/julia-1-2-in-nextjournal/27801)

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**Author:** [@sdanisch](https://discourse.julialang.org/u/sdanisch)\
**Replies:** 8\
**Last updated:** [July 12, 2020, 2:46am UTC](https://discourse.julialang.org/t/julia-1-2-in-nextjournal/27801 "2020-07-12T02:46:28Z")

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Hi everyone, I’m happy to announce that Nextjournal updated all default images to Julia 1.2! Any new article with Julia code cells will now default to this image. There is also a collection with more images that come wi…

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## [\[ANN\] LoggingFacilities.jl - easier transformations](https://discourse.julialang.org/t/ann-loggingfacilities-jl-easier-transformations/42912)

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**Author:** [@tk3369](https://discourse.julialang.org/u/tk3369)\
**Replies:** 0\
**Last updated:** [July 12, 2020, 1:51am UTC](https://discourse.julialang.org/t/ann-loggingfacilities-jl-easier-transformations/42912 "2020-07-12T01:51:11Z")

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Hi! Today, I would like to announce a new package LoggingFacilities.jl. It’s somewhat experimental at the moment but I would like to hear any feedbacks/thoughts. :hammer: What is it? I love LoggingExtras.jl because it…

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## [Simultaneous internode I/O and compute using DistributedArrays?](https://discourse.julialang.org/t/simultaneous-internode-i-o-and-compute-using-distributedarrays/42910)

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**Author:** [@Matt\_Davis](https://discourse.julialang.org/u/Matt_Davis)\
**Replies:** 0\
**Last updated:** [July 12, 2020, 12:40am UTC](https://discourse.julialang.org/t/simultaneous-internode-i-o-and-compute-using-distributedarrays/42910 "2020-07-12T00:40:22Z")

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I am attempting to implement multinode tensor contraction, and I am running in to some issues. My current approach is, given two input tensors A and B and an output tensor C (all DArrays), to spawn on each worker a loop…

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## [ArchGDAL.jl install error,](https://discourse.julialang.org/t/archgdal-jl-install-error/42761)

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**Author:** [@zhangliye](https://discourse.julialang.org/u/zhangliye)\
**Replies:** 5\
**Last updated:** [July 12, 2020, 12:20am UTC](https://discourse.julialang.org/t/archgdal-jl-install-error/42761 "2020-07-12T00:20:49Z")

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I got the current error after installing ArchGDAL.jl. It works last week, and got the error one today. I have run rm ArchGDAL and run ‘add ArchGDAL’, the error is still the same. using ArchGDAL \[ Info: Precompiling Ar…

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## [Object lifetime problem with CxxWrap and make\_const\_array](https://discourse.julialang.org/t/object-lifetime-problem-with-cxxwrap-and-make-const-array/40991)

<div class="topic-metadata">

**Author:** [@Josiah\_Slack](https://discourse.julialang.org/u/Josiah_Slack)\
**Replies:** 10\
**Last updated:** [July 11, 2020, 10:35pm UTC](https://discourse.julialang.org/t/object-lifetime-problem-with-cxxwrap-and-make-const-array/40991 "2020-07-11T22:35:03Z")

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I’m experimenting with using CxxWrap to connect an existing C++ library to a Julia project. There’s a particular case I’m looking at right now - there’s a C++ object that has a std::vector as a data member which I want t…

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## [Solving sparse matrix using backslash, got MethodError: no method matching lu!](https://discourse.julialang.org/t/solving-sparse-matrix-using-backslash-got-methoderror-no-method-matching-lu/42906)

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**Author:** [@Liang\_Chen](https://discourse.julialang.org/u/Liang_Chen)\
**Replies:** 3\
**Last updated:** [July 11, 2020, 10:05pm UTC](https://discourse.julialang.org/t/solving-sparse-matrix-using-backslash-got-methoderror-no-method-matching-lu/42906 "2020-07-11T22:05:34Z")

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I want to solve a system of equation Ax = b using A\\b where A and b are sparse matrix and vector. Also matrix A is symmetric positive definite. However I got an error says: “ERROR: LoadError: MethodError: no method mat…

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## [Overview of JuliaCon by conference chair Jane Herriman](https://discourse.julialang.org/t/overview-of-juliacon-by-conference-chair-jane-herriman/42901)

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**Author:** [@logankilpatrick](https://discourse.julialang.org/u/logankilpatrick)\
**Replies:** 6\
**Last updated:** [July 11, 2020, 6:01pm UTC](https://discourse.julialang.org/t/overview-of-juliacon-by-conference-chair-jane-herriman/42901 "2020-07-11T18:01:32Z")

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Hey all, if you did not get a chance to check it out yet, our very own @xorJane was featured in a podcast talking about JuliaCon 2020! Make sure to check it out and show some support for Jane and the Julia community. …

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## [Question about time series clustering](https://discourse.julialang.org/t/question-about-time-series-clustering/42895)

<div class="topic-metadata">

**Author:** [@abcde](https://discourse.julialang.org/u/abcde)\
**Replies:** 12\
**Last updated:** [July 11, 2020, 3:00pm UTC](https://discourse.julialang.org/t/question-about-time-series-clustering/42895 "2020-07-11T15:00:22Z")

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using TimeSeriesClustering data\_path=normpath(joinpath(dirname(@\_\_FILE\_\_),"..","数据","测试数据.csv")) #ts\_input\_data = load\_timeseries\_data(data\_path;region="none", T=24, years=\[2016\]) ts\_input\_data = load\_timeseries\_data(dat…

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