Ensure that discontinuous fields are correctly saved in the checkpoint_xdmf method.

[gthyagi]

The checkpoint_xdmf method has been updated to correctly save discontinuous fields.

[Copilot]

Pull Request Overview

This PR updates the checkpoint_xdmf method to distinguish between discontinuous (cell-based) and continuous (node-based) fields, ensuring correct file naming and attribute generation in the XDMF output. Key changes include:

• Adjusting the filename format for mesh-variable HDF5 files.
• Adding a helper function and conditional logic to select between cell_fields and vertex_fields based on the variable’s continuity.
• Adding a comprehensive test to verify that discontinuous fields are correctly saved and referenced.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
tests/test_0005_check_xdmf.py	Introduces tests to check that XDMF files correctly reference HDF5 datasets for mesh fields.
src/underworld3/discretisation.py	Modifies checkpoint_xdmf to support discontinuous fields and updates file naming and data paths.

[Copilot]

The helper function 'get_cell_field_shape' assumes that the expected dataset exists in the HDF5 file. Consider adding error handling to provide a clearer message if the dataset is missing.

[julesghub]

If not cell fields are found what does this return? Is it well handled?

[julesghub]

Looks good - just see how it handles if no cell_fields are defined.

[julesghub]

If not cell fields are found what does this return? Is it well handled?

[gthyagi]

Yes, it is handled properly. not getattr(var, "continuous") or getattr(var, "degree")==0 this will ensure get_cell_field_shape called only for discontinuous or degree=0 mesh variable.

# Determine if data is stored on nodes (vertex_fields) or cells (cell_fields)
if not getattr(var, "continuous") or getattr(var, "degree")==0:
    center = "Cell"
    numItems = get_cell_field_shape(var_filename)
    field_group = "cell_fields"
else:
    center = "Node"
    numItems = numVertices
    field_group = "vertex_fields"

[julesghub]

on second inspection I don't think this function should be called get..._shape. Consider get...._size.

Also can you not define this function in the for var in meshVars loop. This is not a good design. Move the function out of the loop. That will make it much less coupled to the loop.

[gthyagi]

check #328