# Different results in serial and parallel run dolfinx

**URL:** <https://fenicsproject.discourse.group/t/different-results-in-serial-and-parallel-run-dolfinx/4370>\
**Category:** dolfinx\
**Created:** [October 21, 2020, 2:28pm UTC](https://fenicsproject.discourse.group/t/different-results-in-serial-and-parallel-run-dolfinx/4370 "2020-10-21T14:28:08Z")\
**Posts on this page:** 4\
**Page:** 2

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**Author:** ![dokken](https://yyz2.discourse-cdn.com/free1/user_avatar/fenicsproject.discourse.group/dokken/32/1560_2.png) [@dokken](https://fenicsproject.discourse.group/u/dokken)\
**Post date:** [October 26, 2020, 1:06pm UTC](https://fenicsproject.discourse.group/t/different-results-in-serial-and-parallel-run-dolfinx/4370/21 "2020-10-26T13:06:32Z")

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> [@fforteneto](#):
>
> `n_bc.vector.set(1.0)`

Issue is that you need to use ghost update after doing this command.

```auto
    n_bc.vector.ghostUpdate(addv=PETSc.InsertMode.INSERT, mode=PETSc.ScatterMode.FORWARD)

```

as vector is only the dofs owned by the given processor

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**Author:** ![fforteneto](https://yyz2.discourse-cdn.com/free1/user_avatar/fenicsproject.discourse.group/fforteneto/32/264_2.png) [@fforteneto](https://fenicsproject.discourse.group/u/fforteneto)\
**Post date:** [October 26, 2020, 1:18pm UTC](https://fenicsproject.discourse.group/t/different-results-in-serial-and-parallel-run-dolfinx/4370/22 "2020-10-26T13:18:44Z")

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Is necessary add the command after interpolation? (e.g., `u_bc1.interpolate(u_bc_inlet)`)

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<div class="post-metadata">

**Author:** ![dokken](https://yyz2.discourse-cdn.com/free1/user_avatar/fenicsproject.discourse.group/dokken/32/1560_2.png) [@dokken](https://fenicsproject.discourse.group/u/dokken)\
**Post date:** [October 26, 2020, 1:19pm UTC](https://fenicsproject.discourse.group/t/different-results-in-serial-and-parallel-run-dolfinx/4370/23 "2020-10-26T13:19:38Z")

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I do not believe so. To be certain you can add it, it should at least not change anything to something wrong.

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**Author:** ![fforteneto](https://yyz2.discourse-cdn.com/free1/user_avatar/fenicsproject.discourse.group/fforteneto/32/264_2.png) [@fforteneto](https://fenicsproject.discourse.group/u/fforteneto)\
**Post date:** [October 26, 2020, 1:41pm UTC](https://fenicsproject.discourse.group/t/different-results-in-serial-and-parallel-run-dolfinx/4370/24 "2020-10-26T13:41:17Z")

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I add the command after `n_bc.vector.set(1.0)` and it is working, it was not necessary after `u_bc1.interpolate(u_bc_inlet)`. Thank you again!

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