# Parallel Julia's self computing

**URL:** <https://discourse.julialang.org/t/parallel-julias-self-computing/52282>\
**Category:** General Usage\
**Tags:** question\
**Created:** [December 23, 2020, 3:31pm UTC](https://discourse.julialang.org/t/parallel-julias-self-computing/52282 "2020-12-23T15:31:56Z")\
**Posts on this page:** 10\
**Page:** 1

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**Author:** ![marllos](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/marllos/32/205917_2.png) [@marllos](https://discourse.julialang.org/u/marllos)\
**Post date:** [December 23, 2020, 3:31pm UTC](https://discourse.julialang.org/t/parallel-julias-self-computing/52282/1 "2020-12-23T15:31:56Z")

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When I run a longer Julia code, I notice that the 24 cores of the computer are operating. Is this because Julia is running my code with parallel computing? Thanks.

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**Author:** ![maxfreu](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/maxfreu/32/17468_2.png) [@maxfreu](https://discourse.julialang.org/u/maxfreu)\
**Post date:** [December 23, 2020, 3:43pm UTC](https://discourse.julialang.org/t/parallel-julias-self-computing/52282/2 "2020-12-23T15:43:55Z")

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Please give details about the code you run. By default, most code runs single core. I cannot give a more precise answer from such a vague question.

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**Author:** ![marllos](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/marllos/32/205917_2.png) [@marllos](https://discourse.julialang.org/u/marllos)\
**Post date:** [December 23, 2020, 4:01pm UTC](https://discourse.julialang.org/t/parallel-julias-self-computing/52282/3 "2020-12-23T16:01:49Z")

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It is an extensive, complex code, and with some extensive loops. But without any parallel programming.

 ![htop](https://global.discourse-cdn.com/julialang/original/3X/2/2/22e47fb0bafd4c0a400bdcd7001d7afa082690aa.png)

I didn’t take printsc before, but all the cores were idle.

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**Author:** ![maxfreu](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/maxfreu/32/17468_2.png) [@maxfreu](https://discourse.julialang.org/u/maxfreu)\
**Post date:** [December 23, 2020, 4:05pm UTC](https://discourse.julialang.org/t/parallel-julias-self-computing/52282/4 "2020-12-23T16:05:14Z")

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Which packages are you using? Please describe the complex code a bit more.

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**Author:** ![ericphanson](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/ericphanson/32/215186_2.png) [@ericphanson](https://discourse.julialang.org/u/ericphanson)\
**Post date:** [December 23, 2020, 4:07pm UTC](https://discourse.julialang.org/t/parallel-julias-self-computing/52282/5 "2020-12-23T16:07:42Z")

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do you use BLAS operations like matrix multiplication? by default that uses OpenBLAS which is multithreaded by default. You can do

```julia
using LinearAlgebra
BLAS.set_num_threads(4)

```

to change the number of threads used by BLAS operations.

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**Author:** ![marllos](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/marllos/32/205917_2.png) [@marllos](https://discourse.julialang.org/u/marllos)\
**Post date:** [December 23, 2020, 4:14pm UTC](https://discourse.julialang.org/t/parallel-julias-self-computing/52282/6 "2020-12-23T16:14:46Z")

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using LinearAlgebra, SpecialFunctions, PyPlot  
It is difficult to describe the code. In general I calculate eigenvectors and eigenvalues of 100x100 matrices, I do calculations like interpolation, numerical integration, and I repeat these calculations for a certain range of parameters.

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**Author:** ![marllos](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/marllos/32/205917_2.png) [@marllos](https://discourse.julialang.org/u/marllos)\
**Post date:** [December 23, 2020, 4:15pm UTC](https://discourse.julialang.org/t/parallel-julias-self-computing/52282/7 "2020-12-23T16:15:30Z")

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Interesting, but I don’t use BLAS, not directly.

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**Author:** ![ericphanson](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/ericphanson/32/215186_2.png) [@ericphanson](https://discourse.julialang.org/u/ericphanson)\
**Post date:** [December 23, 2020, 4:17pm UTC](https://discourse.julialang.org/t/parallel-julias-self-computing/52282/8 "2020-12-23T16:17:52Z")

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> [@marllos](#):
>
> Interesting, but I don’t use BLAS, not directly.

Ah, well you are probably using it without realizing; things like eigenvalues and eigenvectors generally use BLAS too.

> [@marllos](#):
>
> I calculate eigenvectors and eigenvalues of 100x100 matrices

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**Author:** ![maxfreu](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/maxfreu/32/17468_2.png) [@maxfreu](https://discourse.julialang.org/u/maxfreu)\
**Post date:** [December 23, 2020, 4:29pm UTC](https://discourse.julialang.org/t/parallel-julias-self-computing/52282/9 "2020-12-23T16:29:11Z")

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That nails it I‘d say. Merry Christmas and don‘t work too much! 😉

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**Author:** ![marllos](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/marllos/32/205917_2.png) [@marllos](https://discourse.julialang.org/u/marllos)\
**Post date:** [December 23, 2020, 4:32pm UTC](https://discourse.julialang.org/t/parallel-julias-self-computing/52282/10 "2020-12-23T16:32:28Z")

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Cool, I thought Julia parameterized my code lol. Thanks maxfreu, ericphanson. Merry Christmas to everyone!