peclet 1.4.0 — steady states in a third of the steps, and the force on a body by its name

peclet-flow 1.3.0 · peclet-coupling 1.1.1 · metapackages peclet and peclet-cu13 1.4.0.
Unchanged and still pinned: peclet-dem 1.1.0, peclet-pnm 1.0.3, peclet-voro 1.0.4,
peclet-morton 1.0.2, peclet-geom 1.0.1, peclet-amr 0.2.0 (their commits since their tags touch
docs, scripts or packaging metadata only). peclet-halo / peclet-core 1.4.0 was released on its
own earlier the same day (section below); flow and coupling pin its headers (PECLET_CORE_TAG v1.4.0) and peclet[mpi] now installs it.

peclet-flow 1.3.0

Added

• peclet.flow.march_to_steady(solver, monitor, ...) marches a solver to its steady state and
  returns a MarchResult (converged, steps, accelerated_steps, reason, num_restarts,
  monitor). By default the march is Anderson-accelerated (type II, on the device, through core's
  AndersonCore); accelerate=False is the plain march with the same stop test. On a dense
  staggered bed (φ 0.6, N = 64) it certifies in 93 steps instead of 325, 3.4–3.9× less wall time.
  Staggered Solver, and SolverColocated with the 'ghost' scheme; configurations the
  accelerator cannot take (VoF, variable ρ/μ, moving scenes, cell forces, …) raise with the reason
  and point at accelerate=False.
• diagnostics.set_pressure_bottom_solver('auto' | 'direct' | 'algebraic') (developer tier)
  selects the engine of the agglomerated pressure bottom.

Changed (named numerics changes)

• On GPU backends the pressure multigrid's bottom is solved on the device ('auto', the
  default, selects 'direct' where eligible: single rank, a bottom of at most 8192 cells with at
  most 64 fluid components, solids allowed): an FP64 flexible CG to 1e-5, preconditioned by an
  FP32 block-tridiagonal direct factor refactored once per operator change, with no host transfer.
  It replaces the host GraphAMG bottom there. Bubble column on an RTX 5080: 42.6 → 36.1–37.4 ms
  per step; over 50 steps the fields differ from the GraphAMG bottom by at most 2.7e-14 (relative)
  with identical outer iterations on every step. Host backends and the distributed path keep
  GraphAMG and are bitwise unchanged; 'algebraic' restores the previous engine on a GPU.

Changed

• A faster VoF step with identical results (bitwise on CUDA and host): the parabolic-fit
  curvature fallback runs one GPU team per target cell (core 1.3.2's pvFitTerm / pvFitAccum
  split), and the batched marker-block container's last tier runs on persistent warp teams
  (14.8 → 7.4 ms per call on the bubble column).

Deprecated

• Solver.hydro_force_torque() is deprecated and warns: it is not the force on the bodies.
  It returns the reconstructed surface-traction integral, which under-reads the drag by ~30 % at
  every resolution (traction / reaction 0.685–0.730 over φ 0.008–0.45 and N 24–128; the central
  difference spans the wall, so the deficit is in the viscous part) and a spinning sphere's torque
  by 28–41 %. The force and torque on the bodies is hydro_force_torque_reaction() — the
  discrete momentum reaction, exactly conservative; its torque reads 1.019–1.027 of the exact
  periodic-array value at 6–12 cells per radius. The traction, with its pressure/viscous split,
  is diagnostics.hydro_force_torque_traction(). The old name returns the same array as before
  and raises a DeprecationWarning naming both; it goes at the next major release. A consistent
  traction (from the momentum operator's small-cell-robust wall reconstruction) is planned.

Fixed

• hydro_force_torque() (the traction) applied the index → physical conversion twice under a
  physical domain: 0.019× the reaction at extent 1, 3e-8× at 7.3. Cell units were unaffected.
• enable_vof_momentum together with the VoF marker-block container now raises (in either
  order). Momentum-consistent transport skips the step that advects the markers, so with both on
  every marker stayed frozen while the momentum moved.
• Pinned to core v1.4.0.

Known limitations

• march_to_steady's converged=True certifies stationarity at the given dt: the state passed
  the stop test on consecutive plain steps. It does not certify that a plain march from the initial
  state would reach it. Without advection (Stokes) the steady state is unique. With advection,
  above a flow instability (a wake past its Hopf point) Anderson can converge to an unstable
  steady branch that a time march would never show; check such cases with accelerate=False or by
  stepping on from the result. The stop test assumes no mode decays slower than slow_rate per
  step; where one does it under-reads the remainder (dense bed at rtol 1e-10: ~1.4e-8 from the
  steady state), so treat certificates below ~1e-8 on such geometries as approximate.
• The pressure in sealed fluid pockets is arbitrary. Fluid cells that no open face connects to
  the rest of the flow are out of reach of the pressure projection, so their pressure level is
  undetermined (a dense sphere bed, φ 0.6 at N 64, has 126 such cells in 115 pockets). The force on
  each body and the permeability, from hydro_force_torque_reaction(), are unaffected: they move
  by at most 1e-7. The surface-traction diagnostic diagnostics.hydro_force_torque_traction() is
  affected: per-body forces by about 2e-4 of the force, and on the collocated grid the bed-total
  traction is biased as well. Averages of get_p() that include pocket cells shift by 1e-3 to 4e-3
  of the pressure range for each pressure range by which the pockets are offset. A pocket mask and
  a corrected traction are planned after this release.
• In cell units, cell_centers() and an analytic scene disagree by half a cell. Without an
  extent, cell_centers() returns i + 1/2 (origin 0, spacing 1), while set_scene places cell
  (i, j, k)'s centre at (i, j, k). An SDF sampled on cell_centers() for set_solid and the same
  body given to set_scene are therefore offset by half a cell. With a physical domain (extent=)
  both use origin + (i + 1/2) h and agree. The docstrings now say so; unifying the cell-unit
  convention changes results and is deferred to 2.0.0.

peclet-coupling 1.1.1

• ResolvedCfdDem(force_method="traction") reads flow's diagnostics.hydro_force_torque_traction(),
  and falls back to hydro_force_torque() on flow 1.2.0 and older (no diagnostics namespace).
  The default "reaction" is unchanged.
• Pinned to core v1.4.0.

Metapackages peclet / peclet-cu13 1.4.0

• Pins peclet-flow 1.3.0 / peclet-flow-cu13 1.3.0 and peclet-coupling 1.1.1; [mpi] installs
  peclet-core 1.4.0.
• The PyPI page no longer claims Lees–Edwards boxes for peclet.voro: they existed only in the
  retired half-edge engine.
• The containers install peclet.geom in every image and peclet.amr in peclet-cpu, so the
  images carry the family the container docs describe; the documentation site generates its Python
  API pages from the released peclet-cpu image.

Tested

On the workstation (RTX 5080), 2026-10-03/04, against the host-openmp and nvidia-cuda prefixes with
MPI on:

• peclet-flow 1.3.0: 194 of 194 ctests on each backend (kernel tests, the distributed suite at
  np 1, 2, 4 and one np 8 rung, and the Python tests; the two bench instruments excluded). The
  analytic verifications pass on both: periodic spheres (exact no-slip Stokes), the developing
  channel, and the backward-facing step (reattachment x_r/S = 5.26 and 8.16 at Re_S 100 and 200,
  identical on the two backends).
• peclet-coupling 1.1.1: 3 of 3 on each backend; force_method="traction" runs on flow 1.3.0
  without a DeprecationWarning and fills the pressure/viscous split.
• The quick start on README.md, docs/index.md and the Colab notebook executes against flow
  1.3.0 (N = 32: k = 1.2410e-01), and every peclet call on the doc pages and member READMEs exists.