Structured mesh

Owner: linstabpy.mesh.mesh. Mesh is the structured-grid object.

It holds geometry, SBP derivative operators, filters, dissipation state, and sponge state. Deformation and masking must preserve numerical behavior. Geometry-only optimizations are allowed only when tests prove that derivative operators, filters, weights, and saved outputs remain equivalent.

Files

File	Role
mesh.py	Mesh.create, index maps, masking
sbp.py	Summation-by-parts operators in use
sbp_generator.py	Operator generation for even orders 2, 4, 6, 8
filters.py	Mattsson alpha-filter
fdweights.py	Finite-difference weights

SBP orders 2, 4, 6, 8. The Nyquist mode on curvilinear meshes is damped by the alpha-filter (always on in the driver) and, where the metric cross-terms mix grid-scale content, by operator dissipation. Dissipation on a rectilinear mesh is a different claim; see driver.preflight.metric_cross_coupling.