Version 0.4.0

Added:

• Quadrilateral elements are now supported.
  • The support for quad elements in the legacy FEniCS itself is incomplete and buggy. It has been fixed in DOLFINx, but we do not support the next-gen FEniCS yet. So although extrafeathers already supports arbitrary quad meshes, this functionality is currently practically useful mostly for quad meshes on the unit square.
  • Like in FEniCS itself, mixed meshes (having both quads and triangles) are not supported.
• Add prepare_linear_export. See demo.coupled.main01_flow and demo.boussinesq.main01_solve for usage examples.
• Add quad_to_tri to convert a quad mesh to a triangle mesh in a crossed-diagonal format, by adding a node at each cell center and then replacing each quad by four triangles.
  • Note that emulating quad interpolation this way does not actually interpolate bilinearly; the interpolation remains linear on triangles. This produces minor visual artifacts when compared to actual bilinear interpolation. Still, the result looks ok-ish, and lets mpiplot (ab)use Matplotlib to plot FEM functions on quadrilaterals.
• Add trimesh to triangulate the unit square using equilateral triangles (halves of them at two opposite edges).
• Add minmax to extract the min and max of a FEM field on nodal elements. Modes available for raw, abs, l2 (euclidean length). When running in MPI mode, automatically gathers data from all processes. The data may live on an arbitrary subspace (e.g. a component of a vector field that itself lives on a MixedElement).
• Add renumber_nodes_by_distance. Can set the origin point.
• Add collapse_node_numbering. Like dolfin.FunctionSpace.collapse, but for the extrafeathers internal format (cells list and nodes dict, as produced by all_cells). This is sometimes needed; if curious, see the source code of the meshmagic and plotmagic modules for use cases.
• Add interptest demo, to show interpolation of a bilinear function on the unit square on different element types.
• Add smoothing demo, to show the effects of P1->DP0->P1 (and Q1->DQ0->Q1) projection smoothing. This is a technique to eliminate a symmetric numerical checkerboard oscillation with only minor damage to the actual signal.
• Add Eulerian solid mechanics demo: axially moving Kelvin-Voigt sheet using an Eulerian description, with both dynamic and steady-state solvers.
  • This is actually a small open-source research code into the mechanics of axially moving materials, with applications in the analysis of industrial processes. Placing the code here facilitates co-evolving extrafeathers with features our research team currently actually needs.
  • Quadrilateral elements look nice for this.

Changed:

• Improved support for discontinuous spaces (DP1, DP2, DP3, DQ1, DQ2, and DQ3) in various library functions.
• mpiplot and mpiplot_mesh now support also piecewise constant spaces (DP0 and DQ0).
• mpiplot now rejects input if the function space is not supported, instead of trying to project.
  • This is to ensure a faithful representation.
• Plotting preparation changed; now both mpiplot and mpiplot_mesh can take the prep argument.
  • Both mpiplot_prepare and as_mpl_triangulation generate a prep. These have slightly different options and different use cases.
  • mpiplot takes the output of mpiplot_prepare, and mpiplot_mesh that of as_mpl_triangulation.
• Rename midpoint_refine to refine_for_export, since that's the use, and it handles both degree-2 and degree-3 spaces.
• Rename map_refined_P1 to map_coincident, and generalize it.
  • Now works at least with P1, P2, P3, Q1, Q2, Q3, DP0, DP1, DP2, DP3, DQ0, DQ1, DQ2, and DQ3 spaces.
  • Also, add a squared-distance tolerance option for detecting coincident nodes.