# What does 20 in convectParallel(Mesh, \[u1, u2\], -dt, c, 20) mean

**URL:** <https://community.freefem.org/t/what-does-20-in-convectparallel-mesh-u1-u2-dt-c-20-mean/3931>\
**Category:** General Discussion\
**Created:** [May 22, 2025, 3:53pm UTC](https://community.freefem.org/t/what-does-20-in-convectparallel-mesh-u1-u2-dt-c-20-mean/3931 "2025-05-22T15:53:29Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![zxss](https://avatars.discourse-cdn.com/v4/letter/z/bc8723/32.png) [@zxss](https://community.freefem.org/u/zxss)\
**Post date:** [May 22, 2025, 3:53pm UTC](https://community.freefem.org/t/what-does-20-in-convectparallel-mesh-u1-u2-dt-c-20-mean/3931/1 "2025-05-22T15:53:29Z")

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Does anyone know what 20 denotes in command convectParallel(Mesh, [u1, u2], -dt, c, 20) ?

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**Author:** ![prj](https://avatars.discourse-cdn.com/v4/letter/p/ecae2f/32.png) [@prj](https://community.freefem.org/u/prj)\
**Post date:** [May 22, 2025, 7:11pm UTC](https://community.freefem.org/t/what-does-20-in-convectparallel-mesh-u1-u2-dt-c-20-mean/3931/2 "2025-05-22T19:11:37Z")

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It is a safety parameter.

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**Author:** ![zxss](https://avatars.discourse-cdn.com/v4/letter/z/bc8723/32.png) [@zxss](https://community.freefem.org/u/zxss)\
**Post date:** [May 23, 2025, 9:08am UTC](https://community.freefem.org/t/what-does-20-in-convectparallel-mesh-u1-u2-dt-c-20-mean/3931/3 "2025-05-23T09:08:28Z")

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Many thanks. So I will keep it in case this command won’t work.

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**Author:** ![zxss](https://avatars.discourse-cdn.com/v4/letter/z/bc8723/32.png) [@zxss](https://community.freefem.org/u/zxss)\
**Post date:** [May 29, 2025, 2:41pm UTC](https://community.freefem.org/t/what-does-20-in-convectparallel-mesh-u1-u2-dt-c-20-mean/3931/4 "2025-05-29T14:41:04Z")

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Sorry, I want to ask a further question, if I want to change this parameter, if it is more better if I make it larger or smaller?

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**Author:** ![prj](https://avatars.discourse-cdn.com/v4/letter/p/ecae2f/32.png) [@prj](https://community.freefem.org/u/prj)\
**Post date:** [May 30, 2025, 6:55am UTC](https://community.freefem.org/t/what-does-20-in-convectparallel-mesh-u1-u2-dt-c-20-mean/3931/5 "2025-05-30T06:55:35Z")

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It’s problem dependent. In general, you should not use this function.

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**Author:** ![zxss](https://avatars.discourse-cdn.com/v4/letter/z/bc8723/32.png) [@zxss](https://community.freefem.org/u/zxss)\
**Post date:** [May 30, 2025, 8:42am UTC](https://community.freefem.org/t/what-does-20-in-convectparallel-mesh-u1-u2-dt-c-20-mean/3931/6 "2025-05-30T08:42:03Z")

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Thank you very much for your reply. I think it’s unreliable to use convect command to parallelize NS equation. So I will transfer to use Newton method.