# Correctly setting initial conditions using Expression() in DG problem

**URL:** <https://fenicsproject.discourse.group/t/correctly-setting-initial-conditions-using-expression-in-dg-problem/14918>\
**Category:** Legacy DOLFIN\
**Tags:** dg\
**Created:** [June 7, 2024, 7:14pm UTC](https://fenicsproject.discourse.group/t/correctly-setting-initial-conditions-using-expression-in-dg-problem/14918 "2024-06-07T19:14:44Z")\
**Posts on this page:** 1\
**Showing post:** 2

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**Author:** ![nate](https://yyz2.discourse-cdn.com/free1/user_avatar/fenicsproject.discourse.group/nate/32/17_2.png) [@nate](https://fenicsproject.discourse.group/u/nate)\
**Post date:** [June 7, 2024, 8:49pm UTC](https://fenicsproject.discourse.group/t/correctly-setting-initial-conditions-using-expression-in-dg-problem/14918/2 "2024-06-07T20:49:23Z")

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Maybe I’m missing something crucial, but I’m actually surprised this didn’t throw an error.

See the [source](https://bitbucket.org/fenics-project/dolfin/src/1c52e837eb54cc34627f90bde254be4aa8a2ae17/python/dolfin/fem/projection.py#lines-126:129). Note that it expects a formulation posed only within cell volumes. And consider [Where to find 'project'-function in dolfinx? - #2 by nate](https://fenicsproject.discourse.group/t/where-to-find-project-function-in-dolfinx/9829/2).

The projection operation you’re proposing doesn’t make sense for an operator (`avg(.)`) defined on facets only. I’d suggest you construct your own projection operation as you require.

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