# 3D Rotating Hill problem

**URL:** <https://community.freefem.org/t/3d-rotating-hill-problem/4092>\
**Category:** General Discussion\
**Created:** [October 2, 2025, 4:03am UTC](https://community.freefem.org/t/3d-rotating-hill-problem/4092 "2025-10-02T04:03:55Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![ZZM](https://avatars.discourse-cdn.com/v4/letter/z/35a633/32.png) [@ZZM](https://community.freefem.org/u/ZZM)\
**Post date:** [October 2, 2025, 4:03am UTC](https://community.freefem.org/t/3d-rotating-hill-problem/4092/1 "2025-10-02T04:03:55Z")

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I want to use the DG to solve the **Rotating Hill.** In 2D, I can ues the nTonEdge, So How about in 3D

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**Author:** ![frederichecht](https://yyz2.discourse-cdn.com/flex030/user_avatar/community.freefem.org/frederichecht/32/15_2.png) [@frederichecht](https://community.freefem.org/u/frederichecht)\
**Post date:** [October 3, 2025, 9:09am UTC](https://community.freefem.org/t/3d-rotating-hill-problem/4092/2 "2025-10-03T09:09:22Z")

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see [FreeFem-sources/examples/3d/LapDG3d.md at develop · FreeFem/FreeFem-sources · GitHub](https://github.com/FreeFem/FreeFem-sources/blob/develop/examples/3d/LapDG3d.md)

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**Author:** ![ZZM](https://avatars.discourse-cdn.com/v4/letter/z/35a633/32.png) [@ZZM](https://community.freefem.org/u/ZZM)\
**Post date:** [October 5, 2025, 12:53am UTC](https://community.freefem.org/t/3d-rotating-hill-problem/4092/3 "2025-10-05T00:53:41Z")

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Thanks! And I want to know the explanation of “\*\*nElementonB” ，\*\*because I don’t find it in “FreeFEM-documentation.pdf”

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**Author:** ![frederichecht](https://yyz2.discourse-cdn.com/flex030/user_avatar/community.freefem.org/frederichecht/32/15_2.png) [@frederichecht](https://community.freefem.org/u/frederichecht)\
**Post date:** [October 5, 2025, 8:25am UTC](https://community.freefem.org/t/3d-rotating-hill-problem/4092/4 "2025-10-05T08:25:44Z")

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Yes this in file CHANGELOG.md

- DG formulation in 1d ,2d, 3d:

add integral of all border of element : `intallBE(ThL)` and unified the notation by adding

`intallBE(ThS)` , `intallBE(Th2)`, `intallBE(Th3)`

`nuVertex` of now the vertex number of element in intallBE0d integral

`BoundaryBE`, `InternalBE` to know if border element (BE) is on true boundary of not.

update `nElementonB` in case on no manifold data (value greater \> 2) in meshL, MeshS case ..

add code to use jump, mean, otherside of test function on MeshL case. ( not in mesh3 ) to compute RHS.

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**Author:** ![ZZM](https://avatars.discourse-cdn.com/v4/letter/z/35a633/32.png) [@ZZM](https://community.freefem.org/u/ZZM)\
**Post date:** [October 6, 2025, 12:42am UTC](https://community.freefem.org/t/3d-rotating-hill-problem/4092/5 "2025-10-06T00:42:03Z")

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Thank you very much! So, nElementonB is simliar to nTonEdge, which is equal to the Number of adjacent Element of the current face.

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**Author:** ![frederichecht](https://yyz2.discourse-cdn.com/flex030/user_avatar/community.freefem.org/frederichecht/32/15_2.png) [@frederichecht](https://community.freefem.org/u/frederichecht)\
**Post date:** [October 6, 2025, 7:43am UTC](https://community.freefem.org/t/3d-rotating-hill-problem/4092/6 "2025-10-06T07:43:31Z")

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