# RuntimeError: Found overly constrained point while setting up constraints

**URL:** <https://community.geodynamics.org/t/runtimeerror-found-overly-constrained-point-while-setting-up-constraints/1914>\
**Category:** PyLith\
**Created:** [July 20, 2021, 11:43am UTC](https://community.geodynamics.org/t/runtimeerror-found-overly-constrained-point-while-setting-up-constraints/1914 "2021-07-20T11:43:20Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![luxiaokong](https://avatars.discourse-cdn.com/v4/letter/l/3d9bf3/32.png) [@luxiaokong](https://community.geodynamics.org/u/luxiaokong)\
**Post date:** [July 20, 2021, 11:43am UTC](https://community.geodynamics.org/t/runtimeerror-found-overly-constrained-point-while-setting-up-constraints/1914/1 "2021-07-20T11:43:20Z")

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Dear Pylith team,  
I try to use SimpleDB to rewrite the boundary conditions in examples/3d/hex8/step04.cfg to apply non-uniform velocity boundary conditions that do not change with depth on +x, -x, +y, -y-faces.  
First of all, I gave the velocity boundary condition on the + x and -x-faces, which did not cause any problems, and I got the result I want.  
Then, I continued to give the velocity boundary condition on the + y and -y-faces, resulting in the following error.

 ![2021-07-20 19-35-35 的屏幕截图](https://canada1.discourse-cdn.com/flex036/uploads/geodynamics/original/1X/8bb3323d79b79cf6a5c0ba106002daf63d85fb46.png)  
The rewritten step04.cfg and spatialdb files are attached below:  
[step04.cfg](https://community.geodynamics.org/uploads/short-url/lrExhaiyjfZss8Gh02UT4Mpa75S.cfg) (6.8 KB)  
[test.zip](https://community.geodynamics.org/uploads/short-url/cXvNhoX5zS9DqO3tYNIQfpAV84T.zip) (858 Bytes)  
Thank you in advance.

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**Author:** ![baagaard](https://yyz2.discourse-cdn.com/flex036/user_avatar/community.geodynamics.org/baagaard/32/615_2.png) [@baagaard](https://community.geodynamics.org/u/baagaard)\
**Post date:** [July 20, 2021, 3:32pm UTC](https://community.geodynamics.org/t/runtimeerror-found-overly-constrained-point-while-setting-up-constraints/1914/2 "2021-07-20T15:32:27Z")

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You cannot constrain a degree of freedom with more than 1 boundary condition. If you constrain the x-dof with one BC then you cannot also constrain it with another boundary condition. If you want to constrain both the x and y degrees of freedom on the +x, -z, +y, and -y boundaries, then the boundary conditions cannot overlap on the edges.

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**Author:** ![luxiaokong](https://avatars.discourse-cdn.com/v4/letter/l/3d9bf3/32.png) [@luxiaokong](https://community.geodynamics.org/u/luxiaokong)\
**Post date:** [July 21, 2021, 3:40am UTC](https://community.geodynamics.org/t/runtimeerror-found-overly-constrained-point-while-setting-up-constraints/1914/4 "2021-07-21T03:40:20Z")

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Hi Brad,

Thank you for your fast response.  
I tried to use two db files to assign the velocity boundary conditions to +x,-x-faces and + y,-y-faces, respectively, and they did not coincide on the edges, but I still got the same error.  
How can I achieve this if I want to impose velocity boundary conditions on four boundary surfaces at the same time?

Thanks  
Nick

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**Author:** ![baagaard](https://yyz2.discourse-cdn.com/flex036/user_avatar/community.geodynamics.org/baagaard/32/615_2.png) [@baagaard](https://community.geodynamics.org/u/baagaard)\
**Post date:** [July 21, 2021, 2:57pm UTC](https://community.geodynamics.org/t/runtimeerror-found-overly-constrained-point-while-setting-up-constraints/1914/5 "2021-07-21T14:57:15Z")

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This error almost surely indicates that at least one point is associated with two boundary conditions constraining x and y degrees of freedom. Looking at your `step04.cfg` files, I think this is the only way that you can get that error. The only workaround is to make sure your nodesets that constrain both x and y degrees of freedom don’t share any vertices.

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**Author:** ![luxiaokong](https://avatars.discourse-cdn.com/v4/letter/l/3d9bf3/32.png) [@luxiaokong](https://community.geodynamics.org/u/luxiaokong)\
**Post date:** [July 22, 2021, 1:17am UTC](https://community.geodynamics.org/t/runtimeerror-found-overly-constrained-point-while-setting-up-constraints/1914/6 "2021-07-22T01:17:50Z")

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Dear Brad,

Thanks again, I get the point now.

Nick