# Latest

**URL:** https://discourse.julialang.org/latest.md?page=1358

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

**Page:** 1359

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## [Is it possible to have the last iterator change the fastest in Iterator.product?](https://discourse.julialang.org/t/is-it-possible-to-have-the-last-iterator-change-the-fastest-in-iterator-product/63039)

<div class="topic-metadata">

**Author:** [@curious](https://discourse.julialang.org/u/curious)\
**Replies:** 4\
**Last updated:** [June 16, 2021, 6:11pm UTC](https://discourse.julialang.org/t/is-it-possible-to-have-the-last-iterator-change-the-fastest-in-iterator-product/63039 "2021-06-16T18:11:13Z")

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In Julia’s Iterators.product, the first iterator changes the fastest. Is there an easy way to get elements in an order, so that the last iterator changes the fastest? For example with three sequences, I obtain: res = It…

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## [Speed of internal function](https://discourse.julialang.org/t/speed-of-internal-function/62914)

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**Author:** [@Daniel\_Scheinerman](https://discourse.julialang.org/u/Daniel_Scheinerman)\
**Replies:** 7\
**Last updated:** [June 16, 2021, 6:09pm UTC](https://discourse.julialang.org/t/speed-of-internal-function/62914 "2021-06-16T18:09:30Z")

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I stumbled upon some strange timings today. I’m posting a somewhat minimal below. Essentially it seems that if you write a function that returns a function what you return along with it dramatically effects the speed of …

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## [Assigning in place to avoid allocations](https://discourse.julialang.org/t/assigning-in-place-to-avoid-allocations/63031)

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**Author:** [@lancejnelson](https://discourse.julialang.org/u/lancejnelson)\
**Replies:** 5\
**Last updated:** [June 16, 2021, 4:53pm UTC](https://discourse.julialang.org/t/assigning-in-place-to-avoid-allocations/63031 "2021-06-16T16:53:00Z")

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I’m trying to understand how I can assign in-place to avoid allocations. Here is a simple example: nParticles = 10 L = 4 particles = zeros(nParticles,2) norms = zeros(nParticles)#\[0.0 for i=1:nParticles\] newParticle = …

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## [Is there a package with a function that gives cartesian product of two or more sequences?](https://discourse.julialang.org/t/is-there-a-package-with-a-function-that-gives-cartesian-product-of-two-or-more-sequences/63030)

<div class="topic-metadata">

**Author:** [@curious](https://discourse.julialang.org/u/curious)\
**Replies:** 2\
**Last updated:** [June 16, 2021, 4:31pm UTC](https://discourse.julialang.org/t/is-there-a-package-with-a-function-that-gives-cartesian-product-of-two-or-more-sequences/63030 "2021-06-16T16:31:33Z")

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Package IterTools used to have a product function to create a cartesian product of two or more sequences. Version 1.3.0 of IterTools still has this function, but it appears to be deprecated. Asking for help in the repl r…

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## [Debugging registry-download problem](https://discourse.julialang.org/t/debugging-registry-download-problem/63021)

<div class="topic-metadata">

**Author:** [@stevengj](https://discourse.julialang.org/u/stevengj)\
**Replies:** 3\
**Last updated:** [June 16, 2021, 4:21pm UTC](https://discourse.julialang.org/t/debugging-registry-download-problem/63021 "2021-06-16T16:21:40Z")

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Someone in my group downloaded Julia 1.6.1 onto a Linux cluster and got a vague error when trying to install any package: (@v1.6) pkg\> add Flux Installing known registries into \`~/.julia\` ERROR: could not download http…

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## [Segfault with ccall when the code is loaded as package](https://discourse.julialang.org/t/segfault-with-ccall-when-the-code-is-loaded-as-package/63017)

<div class="topic-metadata">

**Author:** [@barucden](https://discourse.julialang.org/u/barucden)\
**Replies:** 4\
**Last updated:** [June 16, 2021, 3:51pm UTC](https://discourse.julialang.org/t/segfault-with-ccall-when-the-code-is-loaded-as-package/63017 "2021-06-16T15:51:09Z")

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Hi, I found some strange behavior which I am not sure is intended. Maybe I am missing something totally obvious, in which case I apologize. I found the following MWE. First, create a new package ~$ julia (@v1.6) pkg\> g…

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## [Manage spaces in Dataframe/Table column names](https://discourse.julialang.org/t/manage-spaces-in-dataframe-table-column-names/63009)

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**Author:** [@Xeos](https://discourse.julialang.org/u/Xeos)\
**Replies:** 7\
**Last updated:** [June 16, 2021, 3:22pm UTC](https://discourse.julialang.org/t/manage-spaces-in-dataframe-table-column-names/63009 "2021-06-16T15:22:10Z")

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Hi, I discovered Julia recently when looking to improve performances of some processes I was running in Python, and most notably while working with dataframes-like structures. I am currently trying to load data from CSV…

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## [Agents.jl abm\_data\_exploration function returns static image](https://discourse.julialang.org/t/agents-jl-abm-data-exploration-function-returns-static-image/62936)

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**Author:** [@Rajith\_Vidanaarachch](https://discourse.julialang.org/u/Rajith_Vidanaarachch)\
**Replies:** 4\
**Last updated:** [June 16, 2021, 2:21pm UTC](https://discourse.julialang.org/t/agents-jl-abm-data-exploration-function-returns-static-image/62936 "2021-06-16T14:21:10Z")

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Hi, I am moving to Julia for my Agent-Based Modelling needs from NetLogo. However, I am interested in keeping the interactive interface of NetLogo which makes the initial modelling easier. I figured that this could be d…

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## [What is the purpose of the @ symbol in Julia?](https://discourse.julialang.org/t/what-is-the-purpose-of-the-symbol-in-julia/63016)

<div class="topic-metadata">

**Author:** [@calvar](https://discourse.julialang.org/u/calvar)\
**Replies:** 2\
**Last updated:** [June 16, 2021, 1:51pm UTC](https://discourse.julialang.org/t/what-is-the-purpose-of-the-symbol-in-julia/63016 "2021-06-16T13:51:57Z")

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Hi! I am new to Julia and I have seen that some functions like Threads.@threads or @printf are preceded by the @ symbol. Is this some kind of naming convention? What is its purpose? Thank you!

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## [\[ANN\] DescriptorSystems.jl: A package for manipulation of generalized state-space (descriptor) system representations](https://discourse.julialang.org/t/ann-descriptorsystems-jl-a-package-for-manipulation-of-generalized-state-space-descriptor-system-representations/62566)

<div class="topic-metadata">

**Author:** [@andreasvarga](https://discourse.julialang.org/u/andreasvarga)\
**Replies:** 22\
**Last updated:** [June 16, 2021, 1:45pm UTC](https://discourse.julialang.org/t/ann-descriptorsystems-jl-a-package-for-manipulation-of-generalized-state-space-descriptor-system-representations/62566 "2021-06-16T13:45:45Z")

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I’m pleased to announce the release of v1.0 of the package DescriptorSystems.jl for manipulation of descriptor systems. Descriptor systems are the most general models employed to describe linear time-invariant systems u…

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## [No automatic type promotion for parametric structs](https://discourse.julialang.org/t/no-automatic-type-promotion-for-parametric-structs/62664)

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**Author:** [@lungben](https://discourse.julialang.org/u/lungben)\
**Replies:** 8\
**Last updated:** [June 16, 2021, 1:12pm UTC](https://discourse.julialang.org/t/no-automatic-type-promotion-for-parametric-structs/62664 "2021-06-16T13:12:39Z")

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When using different (but convertible) types in a constructor, for “standard” structs the types get converted automatically, e.g. struct Struct1 x:: Float64 y end s1b = Struct1(5, 1) # output: Struct1b(5.0, 1) …

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## [Join the JuliaCon 2021 Event page on Linkedin!](https://discourse.julialang.org/t/join-the-juliacon-2021-event-page-on-linkedin/63006)

<div class="topic-metadata">

**Author:** [@logankilpatrick](https://discourse.julialang.org/u/logankilpatrick)\
**Replies:** 1\
**Last updated:** [June 16, 2021, 1:12pm UTC](https://discourse.julialang.org/t/join-the-juliacon-2021-event-page-on-linkedin/63006 "2021-06-16T13:12:31Z")

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Hey folks, We have a LinkedIn event going right now for JuliaCon: JuliaCon 2021 (free and virtual) | LinkedIn. It would help us immensely if you could join the event and share it with your network by pressing the “Share…

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## [How does the memory model of pyjulia work?](https://discourse.julialang.org/t/how-does-the-memory-model-of-pyjulia-work/62989)

<div class="topic-metadata">

**Author:** [@xiaodai](https://discourse.julialang.org/u/xiaodai)\
**Replies:** 3\
**Last updated:** [June 16, 2021, 12:42pm UTC](https://discourse.julialang.org/t/how-does-the-memory-model-of-pyjulia-work/62989 "2021-06-16T12:42:24Z")

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I am using Julia from Python via pyjulia which has a how it works. But I want to understand if there are performance implications. E.g. if I have a numpy array in python and use it in Julia; is Julia making a copy or us…

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## [Cannot convert an object of type DataFrame to an object of type Array](https://discourse.julialang.org/t/cannot-convert-an-object-of-type-dataframe-to-an-object-of-type-array/61598)

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**Author:** [@valperez](https://discourse.julialang.org/u/valperez)\
**Replies:** 2\
**Last updated:** [June 16, 2021, 12:33pm UTC](https://discourse.julialang.org/t/cannot-convert-an-object-of-type-dataframe-to-an-object-of-type-array/61598 "2021-06-16T12:33:08Z")

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Hi, I have a Data Frame that I want to convert into an Array but Julia gives me the following error: MethodError: Cannot convert an object of type DataFrame to an object of type Array I believe that there has someth…

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## [Algorithm with if...else](https://discourse.julialang.org/t/algorithm-with-if-else/62962)

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**Author:** [@12345\_12345](https://discourse.julialang.org/u/12345_12345)\
**Replies:** 8\
**Last updated:** [June 16, 2021, 10:12am UTC](https://discourse.julialang.org/t/algorithm-with-if-else/62962 "2021-06-16T10:12:30Z")

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I’m newbie in Julia, and after seeing YT free course in my free time I followed 2nd lesson of 3rd week \[julia for nervous beginner\] (with if…else) and I’m trying to write a bigger algorithm with Julia, like this one but …

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## [Lorenz attractor has changed?](https://discourse.julialang.org/t/lorenz-attractor-has-changed/62986)

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**Author:** [@Minimum-Pollution-96](https://discourse.julialang.org/u/Minimum-Pollution-96)\
**Replies:** 1\
**Last updated:** [June 16, 2021, 10:04am UTC](https://discourse.julialang.org/t/lorenz-attractor-has-changed/62986 "2021-06-16T10:04:17Z")

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I feel like the lorenz attractor that’s being plotted on the Julia Plots site has changed. I think it used to look similar to the one in Julialang site. Ignore this if this is just a figment of my imagination. If not, wh…

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## [A macro for automatic output generation](https://discourse.julialang.org/t/a-macro-for-automatic-output-generation/62994)

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**Author:** [@iHany](https://discourse.julialang.org/u/iHany)\
**Replies:** 9\
**Last updated:** [June 16, 2021, 9:50am UTC](https://discourse.julialang.org/t/a-macro-for-automatic-output-generation/62994 "2021-06-16T09:50:54Z")

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Hi you all, suppose I have a function my\_func(args...; kwargs...). For example, function my\_func(a, b) a + b end I would like to manipulate the function with a macro to make a function whose output contains macroe…

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## [Notebooks activates project automatically (when started with binder)](https://discourse.julialang.org/t/notebooks-activates-project-automatically-when-started-with-binder/62944)

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**Author:** [@bennibolm](https://discourse.julialang.org/u/bennibolm)\
**Replies:** 2\
**Last updated:** [June 16, 2021, 7:16am UTC](https://discourse.julialang.org/t/notebooks-activates-project-automatically-when-started-with-binder/62944 "2021-06-16T07:16:37Z")

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Hello everyone, I have a question regarding the answer from ANN: mybinder.org support for Julia 1.x and Project.toml. I added a local Project.toml to the sub folder with the notebooks, but when I start the notebook (vi…

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## [SBML parser](https://discourse.julialang.org/t/sbml-parser/54915)

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**Author:** [@Elmo](https://discourse.julialang.org/u/Elmo)\
**Replies:** 4\
**Last updated:** [June 16, 2021, 7:04am UTC](https://discourse.julialang.org/t/sbml-parser/54915 "2021-06-16T07:04:21Z")

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Is anyone actively working on an SBML parser? I saw this and this but can’t find any status updates. I am busy building a Julia version of Cobrapy (much more expansive than COBRA.jl, which seems to be restricted to distr…

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## [PartitionBy, retaining key](https://discourse.julialang.org/t/partitionby-retaining-key/62820)

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**Author:** [@jzr](https://discourse.julialang.org/u/jzr)\
**Replies:** 4\
**Last updated:** [June 16, 2021, 6:28am UTC](https://discourse.julialang.org/t/partitionby-retaining-key/62820 "2021-06-16T06:28:17Z")

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Is there something like Python’s itertools.groupby, which is like Julia’s Transducers.PartitionBy but yields (partition\_key, partition\_entries) pairs instead of only partition entries? cc @tkf

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## [Does julia have a construct analogous to Racket's parameters?](https://discourse.julialang.org/t/does-julia-have-a-construct-analogous-to-rackets-parameters/62658)

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**Author:** [@Samuel\_Ainsworth](https://discourse.julialang.org/u/Samuel_Ainsworth)\
**Replies:** 11\
**Last updated:** [June 16, 2021, 5:51am UTC](https://discourse.julialang.org/t/does-julia-have-a-construct-analogous-to-rackets-parameters/62658 "2021-06-16T05:51:29Z")

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Racket has this cool thing where you can define implicit values called parameters: 4.13 Dynamic Binding: parameterize. Is there anything analogous in julia? For example, it would be convenient in the implementation of t…

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## [How to create a function that uses an object attribute if it exists](https://discourse.julialang.org/t/how-to-create-a-function-that-uses-an-object-attribute-if-it-exists/62972)

<div class="topic-metadata">

**Author:** [@lpratafe](https://discourse.julialang.org/u/lpratafe)\
**Replies:** 3\
**Last updated:** [June 16, 2021, 2:55am UTC](https://discourse.julialang.org/t/how-to-create-a-function-that-uses-an-object-attribute-if-it-exists/62972 "2021-06-16T02:55:31Z")

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Hey everyone, I believe what I am trying to do is pretty simple, but I couldn’t figure it out by myself, and what I read from the documentation wasn’t very helpful. Also, I did search in the forum but couldn’t find exact…

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## [How to get the current world age inside a generated function?](https://discourse.julialang.org/t/how-to-get-the-current-world-age-inside-a-generated-function/62969)

<div class="topic-metadata">

**Author:** [@marius311](https://discourse.julialang.org/u/marius311)\
**Replies:** 5\
**Last updated:** [June 15, 2021, 10:57pm UTC](https://discourse.julialang.org/t/how-to-get-the-current-world-age-inside-a-generated-function/62969 "2021-06-15T22:57:37Z")

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A generated function I’m writing needs to determine if its allowed to call a function its been passed, or if that would result in a world-age error (in which case it would fall back to something else). As part of this, I…

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## [Real quantum device/noisy simulations](https://discourse.julialang.org/t/real-quantum-device-noisy-simulations/62538)

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**Author:** [@rodpiferreira](https://discourse.julialang.org/u/rodpiferreira)\
**Replies:** 11\
**Last updated:** [June 15, 2021, 10:37pm UTC](https://discourse.julialang.org/t/real-quantum-device-noisy-simulations/62538 "2021-06-15T22:37:06Z")

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Hello everyone! I’ve recently learned about YaoQuantum, and I began to use it to solve differential equations via quantum algorithms. Although the results were quite interesting, I would like to perform the same simulat…

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## [Embed YouTube video in Documenter?](https://discourse.julialang.org/t/embed-youtube-video-in-documenter/54244)

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**Author:** [@lmiq](https://discourse.julialang.org/u/lmiq)\
**Replies:** 4\
**Last updated:** [June 15, 2021, 10:17pm UTC](https://discourse.julialang.org/t/embed-youtube-video-in-documenter/54244 "2021-06-15T22:17:21Z")

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Is it possible to embed a youtube video in a Documenter generated page? Thank you.

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## [Array step index](https://discourse.julialang.org/t/array-step-index/62920)

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**Author:** [@jzr](https://discourse.julialang.org/u/jzr)\
**Replies:** 8\
**Last updated:** [June 15, 2021, 9:59pm UTC](https://discourse.julialang.org/t/array-step-index/62920 "2021-06-15T21:59:18Z")

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There are arrays whose first index isn’t 1. If I want the next value after the first index, is it always x\[begin+1\], or is there a generalization like x\[begin+step\]?

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## [The fastest way to calculate matrix inversion](https://discourse.julialang.org/t/the-fastest-way-to-calculate-matrix-inversion/62892)

<div class="topic-metadata">

**Author:** [@yingqiuz](https://discourse.julialang.org/u/yingqiuz)\
**Replies:** 9\
**Last updated:** [June 15, 2021, 12:14am UTC](https://discourse.julialang.org/t/the-fastest-way-to-calculate-matrix-inversion/62892 "2021-06-15T00:14:32Z")

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Hi all I need to calculate the inverse of a positive definite matrix H of the form H = (X’ \* X + Diagonal(d)). X is a flat matrix, having (dominantly) more columns than rows. d consists of positive, large values. The m…

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## [What's the difference between Float64 and Real? And what is the Real type for?](https://discourse.julialang.org/t/whats-the-difference-between-float64-and-real-and-what-is-the-real-type-for/62971)

<div class="topic-metadata">

**Author:** [@Michael\_Barmann](https://discourse.julialang.org/u/Michael_Barmann)\
**Replies:** 3\
**Last updated:** [June 15, 2021, 9:00pm UTC](https://discourse.julialang.org/t/whats-the-difference-between-float64-and-real-and-what-is-the-real-type-for/62971 "2021-06-15T21:00:31Z")

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Pardon this naive question but: what exactly is the difference between Float64 and Real? For example, say we have: a = \[1.0, 2.0, 3.0\] b = Array{Real,1}(a) When I call typeof() on each, it reports the types as Vector{…

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## [Extend methods from another module while calling the original method within the extended method](https://discourse.julialang.org/t/extend-methods-from-another-module-while-calling-the-original-method-within-the-extended-method/62791)

<div class="topic-metadata">

**Author:** [@iHany](https://discourse.julialang.org/u/iHany)\
**Replies:** 12\
**Last updated:** [June 15, 2021, 7:23pm UTC](https://discourse.julialang.org/t/extend-methods-from-another-module-while-calling-the-original-method-within-the-extended-method/62791 "2021-06-15T19:23:53Z")

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Hi, I wonder if it’s possible to extend a method from another module while calling the original method within the extended method. For example, function MyPkg.myfunc(x; t) # extended method 2\*MyPkg.myfunc(x; u=t)…

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## [Sftp client set timeout value](https://discourse.julialang.org/t/sftp-client-set-timeout-value/62967)

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**Author:** [@bww00](https://discourse.julialang.org/u/bww00)\
**Replies:** 0\
**Last updated:** [June 15, 2021, 6:29pm UTC](https://discourse.julialang.org/t/sftp-client-set-timeout-value/62967 "2021-06-15T18:29:15Z")

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Trying to use ftp client to connect and sftp a file. getting libcurl 28 error can a timeout value be set in the ftpclient.jl Thanks

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