# Julia at Scale

**URL:** https://discourse.julialang.org/c/domain/parallel/34.md?page=15

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**Page:** 16

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## [Trouble with addprocs](https://discourse.julialang.org/t/trouble-with-addprocs/7818)

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**Author:** [@jebej](https://discourse.julialang.org/u/jebej)\
**Replies:** 9\
**Last updated:** [December 18, 2017, 3:26am UTC](https://discourse.julialang.org/t/trouble-with-addprocs/7818 "2017-12-18T03:26:57Z")

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I’m having trouble with addprocs. I have set up passwordless login via a key (though the key still asks for my password, in case that could be the issue, though I doubt it). I also have looked at other posts here but th…

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## [Why Don't Shared Arrays Allow Non-Bit-Types?](https://discourse.julialang.org/t/why-dont-shared-arrays-allow-non-bit-types/6975)

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**Author:** [@Juser](https://discourse.julialang.org/u/Juser)\
**Replies:** 5\
**Last updated:** [December 12, 2017, 7:23pm UTC](https://discourse.julialang.org/t/why-dont-shared-arrays-allow-non-bit-types/6975 "2017-12-12T19:23:43Z")

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It would be extremely useful to have shared arrays of non-bit-types. Automatic differentiation, for example, requires functions to accept \<:Real types, and this makes shared arrays difficult to use within function evalu…

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## [@parallel for and more complex operations](https://discourse.julialang.org/t/parallel-for-and-more-complex-operations/7562)

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**Author:** [@Ferran\_Mazzanti](https://discourse.julialang.org/u/Ferran_Mazzanti)\
**Replies:** 8\
**Last updated:** [December 6, 2017, 6:12pm UTC](https://discourse.julialang.org/t/parallel-for-and-more-complex-operations/7562 "2017-12-06T18:12:38Z")

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Hi, I’m starting to appreciate the benefits and simplicity of @parallel for in my codes… sometimes these really run fast, but I have seen that the operation you can perform on the result of each iteration in the for is …

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## [@parallel constructs](https://discourse.julialang.org/t/parallel-constructs/7460)

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**Author:** [@TomConlin](https://discourse.julialang.org/u/TomConlin)\
**Replies:** 4\
**Last updated:** [December 2, 2017, 11:33pm UTC](https://discourse.julialang.org/t/parallel-constructs/7460 "2017-12-02T23:33:30Z")

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Hope this is the appropriate place to put this, if not please feel free to move it. I am wondering if Julia would accept a PR for additional @parallel macros optimized for Lower (and Upper) Triangular Matrices. The b…

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## [Maybe an area the Julia folks may want to explore](https://discourse.julialang.org/t/maybe-an-area-the-julia-folks-may-want-to-explore/7410)

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**Author:** [@Frank\_Applin](https://discourse.julialang.org/u/Frank_Applin)\
**Replies:** 0\
**Last updated:** [November 30, 2017, 1:47pm UTC](https://discourse.julialang.org/t/maybe-an-area-the-julia-folks-may-want-to-explore/7410 "2017-11-30T13:47:30Z")

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Developers use 750 Raspberry Pi boards as supercomputing testbed

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## [DistributedArrays: unexpected behavior before modifying localpart](https://discourse.julialang.org/t/distributedarrays-unexpected-behavior-before-modifying-localpart/7355)

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**Author:** [@mikeT](https://discourse.julialang.org/u/mikeT)\
**Replies:** 1\
**Last updated:** [November 29, 2017, 4:33pm UTC](https://discourse.julialang.org/t/distributedarrays-unexpected-behavior-before-modifying-localpart/7355 "2017-11-29T16:33:33Z")

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I have been trying to learn enough about distributed arrays to solving a simple PDE in parallel; however, there appears to be an error associated with accessing localpart data right before modifying it. I’m trying to un…

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## [Pmap: does it copy or share arguments across processes?](https://discourse.julialang.org/t/pmap-does-it-copy-or-share-arguments-across-processes/7317)

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**Author:** [@drjoke](https://discourse.julialang.org/u/drjoke)\
**Replies:** 9\
**Last updated:** [November 26, 2017, 4:34pm UTC](https://discourse.julialang.org/t/pmap-does-it-copy-or-share-arguments-across-processes/7317 "2017-11-26T16:34:02Z")

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for (name, security) in dataset.securities push!(arg\_array, (name, data\[name\])) end tuples = pmap(extract\_variables, arg\_array) In the above code, data\[name\]) is a Dict{Int64, Float32} that contains a lot of data. …

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## [Addprocs with ssh does not work on 0.6.1](https://discourse.julialang.org/t/addprocs-with-ssh-does-not-work-on-0-6-1/7253)

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**Author:** [@usefulhyun](https://discourse.julialang.org/u/usefulhyun)\
**Replies:** 3\
**Last updated:** [November 24, 2017, 7:06am UTC](https://discourse.julialang.org/t/addprocs-with-ssh-does-not-work-on-0-6-1/7253 "2017-11-24T07:06:50Z")

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Hi, there! My code works well on 0.6.0. However, after upgrading it to 0.6.1 addprocs function does not work when I create a process on remote machine. I tried to add a kwarg tunnel=true to be addprocs(\[“remotehost”\];…

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## [Does constructing SharedArray always fill the values with zeros?](https://discourse.julialang.org/t/does-constructing-sharedarray-always-fill-the-values-with-zeros/7247)

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**Author:** [@usefulhyun](https://discourse.julialang.org/u/usefulhyun)\
**Replies:** 0\
**Last updated:** [November 22, 2017, 2:21pm UTC](https://discourse.julialang.org/t/does-constructing-sharedarray-always-fill-the-values-with-zeros/7247 "2017-11-22T14:21:09Z")

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Does constructing SharedArray always fill the values with zeros? I have tested on my laptop, all creating returns an object filled with zeros. I wonder if this is guaranteed behavior.

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## [What does data communication via RemoteChannel block?](https://discourse.julialang.org/t/what-does-data-communication-via-remotechannel-block/7218)

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**Author:** [@usefulhyun](https://discourse.julialang.org/u/usefulhyun)\
**Replies:** 1\
**Last updated:** [November 21, 2017, 2:32pm UTC](https://discourse.julialang.org/t/what-does-data-communication-via-remotechannel-block/7218 "2017-11-21T14:32:19Z")

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Hi, there! I use RemoteChannels as Communication Queues between processes. My problem is that tasks who are receiving and sending data via RemoteChannels using put! or take! do not surrender its control until data tra…

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## [Atomic block in @async](https://discourse.julialang.org/t/atomic-block-in-async/7076)

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**Author:** [@Wikunia](https://discourse.julialang.org/u/Wikunia)\
**Replies:** 2\
**Last updated:** [November 15, 2017, 2:02am UTC](https://discourse.julialang.org/t/atomic-block-in-async/7076 "2017-11-15T02:02:04Z")

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I am using my own version of pmap as described here: https://docs.julialang.org/en/stable/manual/parallel-computing#Synchronization-With-Remote-References-1 Is there a way to run some block atomically? I have an array…

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## [Error using sum in DistributedArrays](https://discourse.julialang.org/t/error-using-sum-in-distributedarrays/6651)

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**Author:** [@rveltz](https://discourse.julialang.org/u/rveltz)\
**Replies:** 2\
**Last updated:** [November 11, 2017, 7:08am UTC](https://discourse.julialang.org/t/error-using-sum-in-distributedarrays/6651 "2017-11-11T07:08:38Z")

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Hi, I am seeking some advice for using the following (piece) of code on a cluster. It is a simulation of a particular type of neural network with N neurons. When, for the last result of a paper, I do simulation for N=1…

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## [Parallel for triangular domain](https://discourse.julialang.org/t/parallel-for-triangular-domain/7000)

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**Author:** [@TomConlin](https://discourse.julialang.org/u/TomConlin)\
**Replies:** 0\
**Last updated:** [November 10, 2017, 9:21pm UTC](https://discourse.julialang.org/t/parallel-for-triangular-domain/7000 "2017-11-10T21:21:16Z")

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Apologies for leading with the wall of text, just feeling chuffed at the moment Background: “all v.s. all” comparing elements in a set against all other elements in the set and computing a “distance” between each pai…

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## [How can i use more than one processor - or give tasks to each processor](https://discourse.julialang.org/t/how-can-i-use-more-than-one-processor-or-give-tasks-to-each-processor/6935)

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**Author:** [@leaoshark](https://discourse.julialang.org/u/leaoshark)\
**Replies:** 9\
**Last updated:** [November 9, 2017, 11:00am UTC](https://discourse.julialang.org/t/how-can-i-use-more-than-one-processor-or-give-tasks-to-each-processor/6935 "2017-11-09T11:00:34Z")

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Hello Guys … I am tryng to use parallel computing in julia I have to ideas …one is try to set more processors in julia starting ( i do not know how to do that using ATOM ) . or set a task to each processor … for exa…

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## [Branch and Bound](https://discourse.julialang.org/t/branch-and-bound/6860)

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**Author:** [@Wikunia](https://discourse.julialang.org/u/Wikunia)\
**Replies:** 1\
**Last updated:** [November 3, 2017, 9:42pm UTC](https://discourse.julialang.org/t/branch-and-bound/6860 "2017-11-03T21:42:39Z")

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I’m a beginner in parallel computing and would like to get some ideas. My project is branch and bound and I’m wondering what the best parallel computing structure is. I have list of open branch nodes. What is the best …

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## [How to access the localpart of a distributed array?](https://discourse.julialang.org/t/how-to-access-the-localpart-of-a-distributed-array/6711)

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**Author:** [@xiaodai](https://discourse.julialang.org/u/xiaodai)\
**Replies:** 8\
**Last updated:** [October 28, 2017, 5:37am UTC](https://discourse.julialang.org/t/how-to-access-the-localpart-of-a-distributed-array/6711 "2017-10-28T05:37:40Z")

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I was trying to learn distributed array. And I can distribute the arrays using distribute, however I can’t work out how to get the localparts of arrays. As a MWE here what I am trying to do addprocs() @everywhere using…

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## [Distributed Conjugate Gradient Numerical Errors](https://discourse.julialang.org/t/distributed-conjugate-gradient-numerical-errors/6602)

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**Author:** [@klowrey](https://discourse.julialang.org/u/klowrey)\
**Replies:** 9\
**Last updated:** [October 22, 2017, 9:03pm UTC](https://discourse.julialang.org/t/distributed-conjugate-gradient-numerical-errors/6602 "2017-10-22T21:03:46Z")

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Hi All, I was implementing a distributed conjugate gradient method in the course of my research and have run into a numerical issue when distributing the code to multiple processes. Algorithmically, my single process an…

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## [Read(“count\_heads.jl”, String) conversion error](https://discourse.julialang.org/t/read-count-heads-jl-string-conversion-error/6253)

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**Author:** [@EconometricsBySimula](https://discourse.julialang.org/u/EconometricsBySimula)\
**Replies:** 8\
**Last updated:** [October 9, 2017, 3:43am UTC](https://discourse.julialang.org/t/read-count-heads-jl-string-conversion-error/6253 "2017-10-09T03:43:36Z")

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I am going through Parallel Loops and Maps and I am seeming to have difficulty with even accessing the file count\_heads.jl I saved it in my working directory function count\_heads(n) c::Int = 0 for i = 1:n c += rand…

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## [Run model runs in a parallel for loop in julia](https://discourse.julialang.org/t/run-model-runs-in-a-parallel-for-loop-in-julia/6326)

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**Author:** [@Simon\_Besnard](https://discourse.julialang.org/u/Simon_Besnard)\
**Replies:** 2\
**Last updated:** [October 8, 2017, 6:56pm UTC](https://discourse.julialang.org/t/run-model-runs-in-a-parallel-for-loop-in-julia/6326 "2017-10-08T18:56:36Z")

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I am trying to parallelize the code below. The idea is to run several model runs in parallel and push their output in to a single dataframe (i.e. dout). The code I have created works with no parrallelisation so far. Howe…

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## [Parallelization of simple loop: reductions, thread-private variables?](https://discourse.julialang.org/t/parallelization-of-simple-loop-reductions-thread-private-variables/5051)

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**Author:** [@antoine-levitt](https://discourse.julialang.org/u/antoine-levitt)\
**Replies:** 9\
**Last updated:** [September 30, 2017, 9:52pm UTC](https://discourse.julialang.org/t/parallelization-of-simple-loop-reductions-thread-private-variables/5051 "2017-09-30T21:52:37Z")

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Hi, I’m looking for a way to parallelize a simple loop I have. I don’t want to get into the complexity of distributed computing, but I’d like something similar to OpenMP. My code structure is basically similar to this: …

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## [Bug or wrong code?](https://discourse.julialang.org/t/bug-or-wrong-code/5908)

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**Author:** [@Yaroslav\_Kavenchuk](https://discourse.julialang.org/u/Yaroslav_Kavenchuk)\
**Replies:** 0\
**Last updated:** [September 15, 2017, 1:33pm UTC](https://discourse.julialang.org/t/bug-or-wrong-code/5908 "2017-09-15T13:33:36Z")

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echo-server.jl: @everywhere function parallel\_echo\_server(port::Int=8080; debug::Bool=false) (port, server) = listenany(port) debug && println(STDERR, "\[SERVER\] Server started!") n = nprocs() while true let …

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## [How do computation while transferring data between processes](https://discourse.julialang.org/t/how-do-computation-while-transferring-data-between-processes/5722)

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**Author:** [@usefulhyun](https://discourse.julialang.org/u/usefulhyun)\
**Replies:** 0\
**Last updated:** [September 5, 2017, 8:50am UTC](https://discourse.julialang.org/t/how-do-computation-while-transferring-data-between-processes/5722 "2017-09-05T08:50:08Z")

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Hi, there I do data tranferring via RemoteChannel. But I found it is impossible that Julia process run sending, receiving and computation at once. RemoteChannel has its own process and its ID which is determined by an…

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## [Inappropriate memory allocation?](https://discourse.julialang.org/t/inappropriate-memory-allocation/5707)

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**Author:** [@juliohm](https://discourse.julialang.org/u/juliohm)\
**Replies:** 24\
**Last updated:** [September 4, 2017, 3:33pm UTC](https://discourse.julialang.org/t/inappropriate-memory-allocation/5707 "2017-09-04T15:33:42Z")

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I don’t know why this is happening, but this is what track-allocation is giving me: - """ - EuclideanDistance - - The Euclidean distance ||x-y||₂ - """ - struct Eucli…

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## [TopNode not defined when trying to use ParallelAccelerator](https://discourse.julialang.org/t/topnode-not-defined-when-trying-to-use-parallelaccelerator/5714)

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**Author:** [@Naelson\_douglas](https://discourse.julialang.org/u/Naelson_douglas)\
**Replies:** 0\
**Last updated:** [September 4, 2017, 2:18pm UTC](https://discourse.julialang.org/t/topnode-not-defined-when-trying-to-use-parallelaccelerator/5714 "2017-09-04T14:18:48Z")

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Hello! I’m trying to use ParallelAccelerator(which depends on CompilerTools.jl) on top of Julia 5.2 as in the screenshot attached. But I’m getting the “TopNode not defined error”. I see this error was fixed on versio…

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## [Is it possible to use @simd with multiple variable loop?](https://discourse.julialang.org/t/is-it-possible-to-use-simd-with-multiple-variable-loop/5701)

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**Author:** [@juliohm](https://discourse.julialang.org/u/juliohm)\
**Replies:** 5\
**Last updated:** [September 4, 2017, 12:05am UTC](https://discourse.julialang.org/t/is-it-possible-to-use-simd-with-multiple-variable-loop/5701 "2017-09-04T00:05:12Z")

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Any chance of something like the following work? @simd for i=1:10000, j=1:10000 # do something end

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## [Multi-Node Parallelism](https://discourse.julialang.org/t/multi-node-parallelism/5666)

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**Author:** [@garrett-hagemann](https://discourse.julialang.org/u/garrett-hagemann)\
**Replies:** 3\
**Last updated:** [September 2, 2017, 10:55pm UTC](https://discourse.julialang.org/t/multi-node-parallelism/5666 "2017-09-02T22:55:54Z")

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I’m attempting to use Julia in a multi-node environment. I’m using the Stampede 2 system at TACC. I followed the instructions found here: Building with Intel MKL on a KNL system to get a copy of Julia up and running on t…

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## [Controlling GPIO on a cluster machine](https://discourse.julialang.org/t/controlling-gpio-on-a-cluster-machine/5516)

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**Author:** [@Frank\_Applin](https://discourse.julialang.org/u/Frank_Applin)\
**Replies:** 2\
**Last updated:** [August 22, 2017, 11:23pm UTC](https://discourse.julialang.org/t/controlling-gpio-on-a-cluster-machine/5516 "2017-08-22T23:23:32Z")

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Hi, I have several development boards set up in a Beowulf cluster \[with passwordless ssh\] along with my desktop machine (a Dell Optiplex 755). I have 4 nodes: NODE-DELL755 \[which is the master\], NODE-RPI2 \[a Raspberry P…

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## [Is it possible to short-circuit a parallel for loop?](https://discourse.julialang.org/t/is-it-possible-to-short-circuit-a-parallel-for-loop/5427)

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**Author:** [@anon94023334](https://discourse.julialang.org/u/anon94023334)\
**Replies:** 3\
**Last updated:** [August 17, 2017, 9:56pm UTC](https://discourse.julialang.org/t/is-it-possible-to-short-circuit-a-parallel-for-loop/5427 "2017-08-17T21:56:28Z")

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Consider the following code that mimics short-circuiting any(): function bad\_any(n::Integer) a = rand(Bool, n) for i in a i && return true end return false end Is it possible to parallelize the for loop in…

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## [@everywhere and pmap inside of a function?](https://discourse.julialang.org/t/everywhere-and-pmap-inside-of-a-function/5405)

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**Author:** [@juliohm](https://discourse.julialang.org/u/juliohm)\
**Replies:** 14\
**Last updated:** [August 17, 2017, 5:39pm UTC](https://discourse.julialang.org/t/everywhere-and-pmap-inside-of-a-function/5405 "2017-08-17T17:39:05Z")

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Could you please explain the reason why this code is failing and how I could fix it? This is an example of an embarrassingly parallel loop with no data movement, the easiest thing possible in parallel programming: funct…

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## [Parallelization of estimation loop](https://discourse.julialang.org/t/parallelization-of-estimation-loop/5343)

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**Author:** [@juliohm](https://discourse.julialang.org/u/juliohm)\
**Replies:** 18\
**Last updated:** [August 12, 2017, 11:43pm UTC](https://discourse.julialang.org/t/parallelization-of-estimation-loop/5343 "2017-08-12T23:43:07Z")

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I have a loop that is embarrassingly parallel and in which there is no data movement. What is the best way nowadays to parallelize it in Julia v0.6? Assume I have an iterator type: struct MyIterator length::Int end B…

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