# Does local mesh keep the region number

**URL:** <https://community.freefem.org/t/does-local-mesh-keep-the-region-number/3919>\
**Category:** General Discussion\
**Created:** [May 15, 2025, 7:37pm UTC](https://community.freefem.org/t/does-local-mesh-keep-the-region-number/3919 "2025-05-15T19:37:42Z")\
**Posts on this page:** 3\
**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 15, 2025, 7:37pm UTC](https://community.freefem.org/t/does-local-mesh-keep-the-region-number/3919/1 "2025-05-15T19:37:42Z")

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Dear all,

When I parallelize my fsi code, I have a problem about the mesh region number on each local processor.

In my sequential code, I separate the conforming mesh as fluid(red color) and solid part(black color) as

 ![7ab8b3db27a115620222b7ba121d3a7](https://canada1.discourse-cdn.com/flex030/uploads/freefem/original/2X/e/e0895628fbbc936690cb8e329ba46be08d8f7733.png)

Then after buildDmesh the whole conforming mesh , it is separated by overlapping local meshes(here is 8 processors) as

 ![19aec5cf117a5ee3aed2e2718fb6a4d](https://canada1.discourse-cdn.com/flex030/uploads/freefem/original/2X/6/60bf6f569271cc9fad8f1c36cbd16f21eabdc78e.png)

Since after buildDmesh, my mesh Th used on varf becomes local now

 ![4b8bcf2e437298c239a4195d07e6c17](https://canada1.discourse-cdn.com/flex030/uploads/freefem/original/2X/3/34535bca826ce2ca453cd914f35af96f11bf22ff.png)

My question is that does the local mesh on each processor keep the region number as the whole mesh? For example, for this local mesh, does it keep the region number ?

 ![88174cb188e0fa2336801b71cec4782](https://canada1.discourse-cdn.com/flex030/uploads/freefem/original/2X/8/8195f198c6552ce1cdd37c42a183b759b0d924e2.png)

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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 16, 2025, 8:53am UTC](https://community.freefem.org/t/does-local-mesh-keep-the-region-number/3919/2 "2025-05-16T08:53:02Z")

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Yes, region number are not modified.

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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 16, 2025, 9:01am UTC](https://community.freefem.org/t/does-local-mesh-keep-the-region-number/3919/3 "2025-05-16T09:01:47Z")

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Many thanks. And I find that this post [Large scale FSI example with parallel implementation - #3 by clthu](https://community.freefem.org/t/large-scale-fsi-example-with-parallel-implementation/3460/3) is very helpful for me now in order to parallelise my fsi code.