Hi, CIG Team!

I have an output question with Pylith v2.2.2. How can I output the plane strain of the ground surface in a 3D model? It seems like that the `cell_data_fields`

can not be used in the `[pylithapp.problem.formulation.output.subdomain]`

.

Thanks.

Output on a boundary is restricted to fields that are defined on the boundary. In the case of subdomain output this means only solution fields.

Fields derived from the solution, such as stress and strain, are only defined within a material. Thus they can be output using the material. This means you can get stress and strain at the cells that reach the surface, but not *on the surface*. To be more specific, stress and strain are computed at the quadrature points, which are in the interior of the cell; using cell averaging the result is a single value per cell that is the average over the quadrature points.

Thanks for your reply. Do you mean that only volume strain can be output in a 3D model?

Correct, in 3D we compute the volumetric strain. We always provide the 6 independent components. If you only want the components in the horizontal direction (xx, xy, and yy), then you can simply ignore the other components.

When we say plane strain, we refer to the 2D case where the displacement in the z direction is 0. In most 3D models, the displacement in the z direction is not 0, so plane strain conditions are not met.