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Update tutorials to match the current API - #247

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fix/update-tutorial
Aug 5, 2026
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Update tutorials to match the current API#247
zfergus merged 5 commits into
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fix/update-tutorial

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@zfergus zfergus commented Aug 4, 2026

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Summary

Went through all 11 pages in docs/source/tutorials and verified every code snippet against the current codebase. Verification was mechanical, not by eye: the C++ snippets were extracted into a compile harness (-fsyntax-only against the real headers, one translation unit per snippet so errors attribute precisely) and the Python snippets into a run harness against a built ipctk. 37 C++ snippets compile and 30 Python snippets run, where previously many did neither.

Removed or renamed API the tutorials still used

Tutorial said Actual API
ipc::point_triangle_ccd(...) free function method on NarrowPhaseCCD subclasses (TightInclusionCCD, AdditiveCCD, InexactCCD)
#include <ipc/ccd/ccd.hpp> header no longer exists
ipc::point_point_nonlinear_ccd + 3 siblings NonlinearCCD::point_point_ccd etc.
candidate.ccd(vertices, edges, faces, toi) candidate.ccd(dof(...), dof(...), toi) — takes stencil vertices
build(mesh, v, collisions, B, barrier_stiffness, mu) build(mesh, v, collisions, B, mu)
CollisionMesh(is_on_surface, positions, E, F) gained an orient_vertex mask
ProjectToPSD::CLAMP PSDProjectionMethod::CLAMP (and NONE was undocumented)
candidates.build(..., broad_phase) takes BroadPhase*, needs &broad_phase
ipctk.Collisions() ipctk.NormalCollisions()
collision_mesh.rest_positions() a property, not a method
initial_barrier_stiffness(..., max_barrier_stiffness) returns it instead of taking it

The TangentialCollisions::build one is worth calling out: in C++ the stale call still compiled, silently binding barrier_stiffness to mu_s and mu to mu_k. Anyone copying that snippet got a wrong friction coefficient with no diagnostic.

Code that never worked

Two Python snippets were outright SyntaxError (multi-line assignment without parentheses). Also a missing ; and a stray one, Eigen::MatrixXd where MatrixXi was required, filib::Interval qualified as ipc::Interval, and several undefined or misspelled identifiers (mesh vs collision_mesh, collision vs collisions, map_displacement).

Corrected the conservative-CCD note

The note claimed the returned TOI "is scaled by DEFAULT_CONSERVATIVE_RESCALING". That describes a fallback branch, not the normal path. ccd_strategy instead inflates the minimum separation the query stops at:

min_effective_distance = (1 - conservative_rescaling) * (initial_distance - min_distance);
min_effective_distance = std::min(min_effective_distance, 1e-4);   // <-- usually binds

and only does toi *= conservative_rescaling when that first query returns toi < SMALL_TOI.

The practical consequence is worse than a wording nit: because the 1e-4 cap usually binds, conservative_rescaling of 0.8, 0.5, and 0.1 all return the byte-identical TOI 0.49994993209838867 for the tutorial's own query. Someone tuning that parameter to tighten the result would see nothing change and reasonably conclude the knob was broken. The note now gives the formula, flags the cap, and scopes the TOI-scaling claim to the fallback. The formula was validated against the implementation across 7 configurations, matching to 6 decimal places including nonzero min_distance.

Binding changes

Some Python tabs were unfixable as documentation because the API was not exposed:

  • SmoothCollisions.compute_adaptive_dhat — without this, adaptive dhat was unreachable from Python, even though build() takes use_adaptive_dhat=True and requires this be called first.
  • SmoothContactParameters.adaptive_dhat_ratio property.
  • BarrierPotential.stiffness / .use_physical_barrier properties, mirroring the C++ setters.
  • Renamed SmoothPotentialSmoothContactPotential to match C++. No in-tree users and the package is a 2.0 alpha, so it is a straight rename with no alias.

Verified the new setters reach the evaluation path rather than just storing a field: setting stiffness = 3.0 scales the potential by exactly 3x, and for both use_physical_barrier values the potential, gradient, and Hessian are bit-identical to the constructor form.

Input validation instead of vanishing asserts

BarrierPotential asserts dhat > 0, stiffness > 0, and a non-null barrier, but assert() is compiled out under NDEBUG — so in a release build Python could set dhat = 0 and get undefined behavior instead of an error. The bindings now validate and raise ValueError, following the existing py::value_error convention in common.hpp. assert_positive is written as !(value > 0) so NaN is rejected too. Confirmed against a release (NDEBUG) build that all 15 invalid inputs raise, object state is unchanged after a rejected set, and valid values (including dhat = 1e-300) still pass.

Test plan

  • 37/37 C++ tutorial snippets compile against real headers
  • 30/30 Python tutorial snippets run against a built ipctk
  • 24 existing python/tests pass (test_collision_mesh.py and test_ipc.py fail to collect on current pytest due to yield-style tests — pre-existing, untouched here)
  • nonlinear_ccd.rst literalinclude markers all still resolve; the test they pull from passes
  • clang-format clean; pre-commit hooks pass

🤖 Generated with Claude Code

zfergus and others added 2 commits August 4, 2026 16:28
Several parts of the documented C++ API had no Python equivalent, which made
the GCP and convergent-formulation tutorials impossible to follow from Python:

- Add SmoothCollisions.compute_adaptive_dhat. Without it, adaptive dhat was
  unreachable from Python even though build() accepts use_adaptive_dhat=True
  and requires this to be called first.
- Add SmoothContactParameters.adaptive_dhat_ratio property.
- Add BarrierPotential.stiffness and .use_physical_barrier properties,
  mirroring set_stiffness()/set_use_physical_barrier() in C++.

Rename the Python SmoothContactPotential class from "SmoothPotential" to
match the C++ name. It had no in-tree users and the package is still a 2.0
alpha, so this is a straight rename with no alias.

Validate preconditions in the bindings rather than relying on the C++
asserts. BarrierPotential asserts dhat > 0, stiffness > 0, and a non-null
barrier, but assert() is compiled out under NDEBUG, so a release build would
silently accept a bad value and produce undefined behavior. The bindings now
raise ValueError, following the existing py::value_error convention in
common.hpp. The new assert_positive helper is written as !(value > 0) so NaN
is rejected as well.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Verified every snippet in docs/source/tutorials by extracting the C++ into a
compile harness (-fsyntax-only against the real headers) and running the
Python against a built ipctk. Both now pass end to end.

Removed/renamed API the tutorials still used:

- ipc::point_triangle_ccd and the other free narrow-phase functions are now
  methods on NarrowPhaseCCD subclasses; <ipc/ccd/ccd.hpp> no longer exists.
- The four *_nonlinear_ccd free functions are now NonlinearCCD methods.
- CollisionStencil::ccd takes stencil vertices, not (vertices, edges, faces);
  use dof() to gather them.
- TangentialCollisions::build no longer takes barrier_stiffness. In C++ the
  stale call still compiled, silently binding barrier_stiffness to mu_s and
  mu to mu_k. Stiffness now comes from the normal potential.
- CollisionMesh gained an orient_vertex mask, so the 4-argument
  construct_is_on_surface form no longer compiles.
- ProjectToPSD is now PSDProjectionMethod (and NONE was undocumented).
- Candidates::build takes a BroadPhase*, so the C++ call needs &broad_phase.
- ipctk.Collisions does not exist; rest_positions is a property, not a method;
  initial_barrier_stiffness returns max_barrier_stiffness instead of taking it.

Also fixed code that never worked: two Python snippets were SyntaxErrors
(multi-line assignment without parentheses), a missing semicolon and a stray
one, MatrixXd where MatrixXi/MatrixXd was required, filib::Interval qualified
as ipc::Interval, and various undefined or misspelled identifiers (mesh vs
collision_mesh, collision vs collisions, map_displacement).

Corrected the note on conservative CCD. TightInclusionCCD does not scale the
returned TOI in the normal path; it inflates the minimum separation the query
stops at, capped at 1e-4, and only scales the TOI in the fallback taken when
that query returns a TOI below SMALL_TOI. Because the cap usually binds,
changing conservative_rescaling often has no effect on the result at all,
which the previous wording actively obscured.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Copilot AI lite review requested due to automatic review settings August 4, 2026 21:29

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Pull request overview

Updates the Sphinx tutorials to match the current IPC Toolkit C++/Python APIs and extends the Python bindings where needed so that documented workflows (adaptive dhat, barrier parameter setters) are actually usable and fail safely in release builds.

Changes:

  • Refactors multiple tutorial snippets to align with renamed/moved APIs (CCD, collision sets, collision mesh masks, PSD projection enum, candidates broad-phase pointer usage, etc.).
  • Improves Python bindings for smooth contact / barrier potential (exposes SmoothCollisions.compute_adaptive_dhat, SmoothContactParameters.adaptive_dhat_ratio, BarrierPotential setters and validation).
  • Clarifies Tight Inclusion CCD conservativeness behavior in docs (distance inflation vs TOI scaling fallback).

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 2 comments.

Show a summary per file
File Description
python/src/potentials/barrier_potential.cpp Adds Python-side validation and new/renamed bindings (BarrierPotential validation, SmoothContactParameters.adaptive_dhat_ratio, SmoothContactPotential rename).
python/src/common.hpp Introduces reusable Python-binding validation helpers (assert_positive, assert_not_none).
python/src/collisions/normal/normal_collisions.cpp Exposes SmoothCollisions.compute_adaptive_dhat to Python with docs and default args.
docs/source/tutorials/simulation.rst Fixes tutorial code to use current mesh/collision/potential APIs and corrects types/identifiers.
docs/source/tutorials/ogc.rst Updates tutorial snippets to pass collision_mesh where the API expects it (C++/Python).
docs/source/tutorials/nonlinear_ccd.rst Updates nonlinear CCD documentation to the NonlinearCCD class API and fixes interval type qualification.
docs/source/tutorials/getting_started.rst Updates examples for current CCD APIs, collisions class names, collision mesh properties, candidates build signatures, and improves CCD note accuracy.
docs/source/tutorials/gcp.rst Updates docs to reference new Python property access for adaptive dhat ratio.
docs/source/tutorials/convergent.rst Updates convergent formulation tutorial to use NormalCollisions and BarrierPotential.use_physical_barrier consistently (C++/Python).
docs/source/tutorials/adhesion.rst Fixes minor tutorial snippet correctness (e.g., missing semicolon, updated tangential collisions build signature).

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Comment thread python/src/common.hpp
Comment thread python/src/potentials/barrier_potential.cpp
@zfergus zfergus added this to the v1.6.1 milestone Aug 4, 2026
zfergus and others added 3 commits August 4, 2026 17:19
The input validation and newly exposed APIs added in 6a34858 had no automated
coverage, so a regression would have been silent.

Uses unittest.TestCase rather than plain functions so assertRaises is available
under both nose2 (the CI runner) and pytest, without adding a pytest dependency.

Covers:

- BarrierPotential validation: ctor and setters reject <= 0 and NaN for dhat
  and stiffness, and None for barrier. Also asserts object state is unchanged
  after a rejected assignment, and that tiny-but-positive values still pass.
- BarrierPotential.stiffness reaches the evaluation path, not just a stored
  field: tripling it triples the potential and gradient.
- BarrierPotential.use_physical_barrier via the property is equivalent to the
  ctor kwarg for potential, gradient, and Hessian, plus a companion test that
  the flag changes the result at all so that equivalence is not vacuous.
- SmoothCollisions.compute_adaptive_dhat as a differential pair: a baseline
  test pins that this mesh/dhat combination produces spurious nonzero forces
  at rest without adaptive dhat, and the adaptive test asserts they are exactly
  zero with it. The baseline is what keeps the second test meaningful.
- SmoothContactParameters.adaptive_dhat_ratio round-trips and actually reaches
  compute_adaptive_dhat: larger ratios activate monotonically more collisions
  in a deformed configuration.
- The SmoothContactPotential rename, guarded in both directions.

Verified the tests bite by mutation testing: reverting the ctor validation, the
setter validation, and the adaptive_dhat_ratio setter (to a no-op) turns them
red, while the untouched barrier-ctor overload keeps passing, so the failures
are specific rather than blanket.

Potential/gradient/Hessian comparisons use a relative tolerance rather than
exact equality, since the sums are parallel reductions whose operand order is
not reproducible.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
The Narrow-Phase section ended with "The alternatives are AdditiveCCD and
InexactCCD", which was wrong in three ways:

- InexactCCD is behind IPC_TOOLKIT_WITH_INEXACT_CCD, which defaults to OFF, so
  it does not exist in a default build and is absent from the Python module.
  Now marked opt-in, matching the wording already used in cpp-api/ccd.rst.
- It implied a difference in conservatism policy between the three that does not
  exist. All three compute their margin as dmin + (1-r)(d0 - dmin);
  TightInclusionCCD alone caps the second term at 1e-4, which is the entire
  reason it reports a time of impact closer to the exact one for the same query.
- It said nothing about AdditiveCCD's actual trade-off.

For AdditiveCCD, lead with the strength (>100x faster, reliable in practice) and
keep the theoretical caveat subordinate: it does not account for rounding error
in its distance computations, but the default 10% margin is large enough to avoid
false negatives, at the cost of a less accurate time of impact and more false
positives. The failure mode is shrinking that margin, i.e. pushing
conservative_rescaling toward 1.0 — not ordinary use.

Also note that the margin is a fraction of the initial separation in excess of
dmin rather than of the raw distance. That distinction comes from the identity
documented on the gap computation in additive_ccd.cpp, (d - xi) =
(d^2 - xi^2) / (d + xi), and it is not cosmetic: for a large minimum separation
the two readings differ by an order of magnitude.

Normalize d_\text{min} to d_\min, the convention already used elsewhere in the
tutorials.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.58%. Comparing base (57344ee) to head (f286192).

Additional details and impacted files
@@           Coverage Diff           @@
##             main     #247   +/-   ##
=======================================
  Coverage   96.58%   96.58%           
=======================================
  Files         163      163           
  Lines       16673    16668    -5     
  Branches      922      922           
=======================================
- Hits        16103    16099    -4     
+ Misses        570      569    -1     
Flag Coverage Δ
unittests 96.58% <ø> (+<0.01%) ⬆️

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@zfergus
zfergus merged commit 3c317b5 into main Aug 5, 2026
21 checks passed
@zfergus
zfergus deleted the fix/update-tutorial branch August 5, 2026 06:10
zfergus added a commit that referenced this pull request Sep 3, 2026
…#249)

* Template all distance functions for scalar type

- Refactored all geometric distance, gradient, and hessian functions to
  be
  templated on scalar type (e.g., double, float).
- Updated Python bindings to explicitly instantiate with double.
- Removed point_point.cpp, moved implementation to header as inline
  template.
- Updated all usages and tests to use templated versions.
- Added Eigen expression overloads for point-point distance functions.
- Updated normal and normalization utilities to be templated.
- Set minimum C++ standard to C++20 in CMakeLists.txt.

* Refactor smooth contact distance code to use unified distance functions

- Remove redundant point/edge/triangle distance implementations from
  smooth_contact/distance
- Replace calls to local *_sqr_distance with core distance functions
- Update includes to use ipc/distance/point_line.hpp and related headers
- Simplify mollifier and primitive_distance to use unified API
- Minor cleanup in tangential_potential and point_plane distance math

* Ensured all arithmetic in auto-generated and hand-written code uses the
templated type for numeric literals

* Templatize barrier functions and classes for float/double support

- Convert barrier functions and barrier class hierarchy to use templates
- Update all usages to specify template parameters where needed
- Update Python bindings and tests to construct template barrier types
- Extend benchmarks to compare float and double barrier performance
- Improves support for mixed-precision and SIMD optimizations

* Replace EigenExpression concept with typename

- Set default CMAKE_CXX_STANDARD to 17 for top-level projects
- Comment out EigenExpression concept in utils/eigen_ext.hpp
- Update Eigen-expression wrapper templates to use typename
  parameters and add enable_if where appropriate

* Fix template scalar typedef in edge-edge

* Fix float precision and explicit-scalar calls in the templated distance API

Scale PARALLEL_THRESHOLD in edge_edge_distance_type with the precision of T.

u x v cancels for nearly parallel edges, leaving an absolute error of about
eps*|u|*|v| per component, so sin^2(theta) cannot be resolved below ~eps^2.
The threshold was left as a hard-coded 2.5e-16, which is ~1.13*eps for double
but sits ~57x *below* float's noise floor, making the near-parallel branch
unreachable in single precision. Over 20k exactly-parallel edge pairs the
float distance type disagreed with the double one 44% of the time, and
edge_edge_distance<float> differed from the double result by >0.1% relative
in 14.8% of cases (worst case 24x). Both drop to 0% after the fix.

The threshold is now derived from the double-tuned value by the ratio of
epsilons, so the double threshold is bit-for-bit unchanged (asserted); only
the newly added float instantiation changes. parallel_tolerance is typed T
rather than double to match.

Guard the *_distance_type EigenExpression wrappers with std::is_class_v.

The other wrappers are rejected by SFINAE when the first template argument is
given explicitly as a scalar, because their trailing return type mentions
typename DerivedX::Scalar. These four return a non-dependent enum, so nothing
rejected the candidate and substitution went on to form Eigen::MatrixBase<T>,
a hard error inside Eigen rather than a substitution failure. As a result
edge_edge_distance_type<double>(a, b, c, d) -- the natural way to pick the
scalar in the new templated API -- failed to compile with 20 errors pointing
into Eigen internals. The guard matches the one already used on the
single-argument wrappers in geometry/normal.hpp.

Drop the commented-out EigenExpression concept and its now-unused <concepts>
include. The doc comment left above it described a dispatch contract the
shipped code does not follow ("Layer 1 always calls Layer 2 with explicit
<T>"), which is exactly the gap that produced the compile failure above.

Fix the sizes in the MatrixMax alias doc comments: MatrixMax2f/MatrixMax2d
were documented as 3x3 and MatrixMax9f/MatrixMax9d as 12x12.

Add a v2.0.0 (alpha) section to the release notes covering the scalar
templatization of the distance, barrier, and normal APIs, along with every
commit since v1.6.0: the Tight Inclusion 1.1.0 update (#248), the tutorial
and Python binding work (#247), the edge-triangle intersection coordinates
and CollisionMesh::face_normals (#245), the mollified m == 0 Hessian PSD
projection fix (#244), and the MeshFEM gallery entry.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

* Split the distance API into deducing front ends over fixed-size kernels

The distance functions now have two layers. The concrete kernels moved into
ipc::detail, templated on <typename T, int dim> (or just <typename T> for the
3D-only line_line, edge_edge, and point_triangle) and taking
Eigen::ConstRef<Eigen::Vector<T, dim>>. The public names in ipc are thin front
ends templated on the argument expression types: they deduce the scalar,
resolve the dimension at compile time when the caller's type knows it, and
otherwise take a single runtime branch on size(). Existing calls are
unaffected.

The win is the dimension, not the parameter passing. Erasing a Vector3d into a
VectorMax3d cost 2.4x, so the front end branches on size() before it
materializes anything and the fixed-size path never forms a dynamically sized
temporary. Measured on the dominant in-tree call site, a row of a column-major
MatrixXd:

  point_line_distance                8.2 -> 2.3 ns   3.5x
  point_edge_distance, AUTO         18.1 -> 5.2 ns   3.5x
  point_triangle_distance, AUTO     93.3 -> 12.8 ns  7.3x
  point_point_distance_hessian                       5x
  normalization_and_jacobian                         3.4x

point_triangle_distance_type is the largest single piece of that: its three
2x2 LDLT solves are replaced by a closed form, since each edge lies in the
triangle's plane and the Gram matrix is therefore diagonal. An error study
over 10.8M configurations found no classification changes outside triangles
collinear to within 1e-11 of their own edge length, a regime where the old
code's own answer flips under a one-ulp input perturbation. It also fixes two
real failures: above coordinate scale ~1e+51 the LDLT returned an infinite
plane distance on every query, and in float near 1e-6 Eigen's tolerance
discarded denormal Gram entries (2771 misclassifications per 400k, now 0).

Two smaller levers, both measured: moving the cold throw bodies out of line
behind [[noreturn]] helpers (worth up to 2x on its own, since constructing a
std::invalid_argument inline consumes the caller's inlining budget), and
branching once on the dimension in EdgeVertexCandidate (3.1x on the gradient).
edge_edge_distance and point_triangle_distance keep their out-of-line switch
dispatch; inlining a 9- or 7-case switch measured as a 10% regression with
runtime distance types.

line_line_distance_gradient and line_line_distance_hessian are single
MatrixBase templates rather than two layers. They read three coefficients per
argument and hand them to generated code, so Eigen::ConstRef's guaranteed
single evaluation buys nothing and its materialization of an expression
argument costs 1.16x.

Also:

- Guard the *_distance_type Eigen-expression overloads with std::is_class_v.
  Their return type is a non-dependent enum, so an explicit scalar argument
  was not rejected by SFINAE and instead formed Eigen::MatrixBase<double>, a
  hard error inside Eigen.
- Scale PARALLEL_THRESHOLD in edge_edge_distance_type with the precision of
  the scalar type. The value tuned for double sits ~57x below the cancellation
  noise floor of u x v in single precision, making the near-parallel branch
  unreachable for float: across 20k exactly-parallel edge pairs the float
  distance type disagreed with the double one 44% of the time. The double
  threshold is bit-for-bit unchanged.
- Taking the address of these functions is no longer possible, so the Python
  bindings wrap them in lambdas.
- Rewrite tests/src/tests/benchmark_eigen.cpp around the shipped design:
  every row now compares the library against a same-TU reference
  implementation that acts as a noise-floor control, and the accumulated
  findings and measurement traps are consolidated into one header block. This
  drops a benchmark helper that asked for block<3,1> from a 1x3 row
  expression, reading out of bounds under NDEBUG.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

* Unify the non-floating-point distance-type guard and the autogen instantiations

Two cleanups in the templated distance API.

`edge_edge` and `point_triangle` guarded their AUTO resolution with
`is_same_v<T, double> || is_same_v<T, float>` and then let AUTO fall through
to the switch, where the default case threw the generic "invalid distance
type". `point_edge` instead used `is_floating_point_v<T>` with an explicit
`throw_auto_requires_explicit_dtype`. Adopt the latter everywhere, naming the
function in the message, so a scalar type that cannot resolve a distance type
now reports why rather than claiming its distance type is invalid:

    edge_edge_distance: an explicit distance type is required for
    non-floating-point scalars; ...

This is a user-visible improvement for autodiff scalars, which reach these
paths today. It also covers the gradient and Hessian kernels, whose AUTO
resolution was previously unguarded, so they can now be instantiated for
scalar types that have no ordering.

The generated `autogen` instantiations in `line_line`, `point_line`, and
`point_plane` spelled out every signature once per scalar type -- eight
hand-written lines in `point_line`, whose four functions take 6, 9, 6 and 9
arguments and fill arrays of 6, 9, 36 and 81. Fold each file's list into an
`IPC_INSTANTIATE_*_AUTOGEN(T)` macro, matching the convention already used for
the distance kernels themselves. `nm` confirms the same sixteen `float` and
`double` symbols are still emitted.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

* Name every unsupported scalar family in the AUTO distance-type error

The message claimed "the distance type cannot be determined from an autodiff
scalar", which predates the other scalar types that reach this path. It is now
also hit by SIMD batches and by filib::Interval, for which the old wording was
simply wrong. Say what the actual obstacle is -- resolving AUTO means comparing
single ordered values -- and name all three families.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

* Extend the two-layer template design across the remaining geometry kernels

Convert every remaining per-collision kernel family to the shape the distance
functions established: fixed-size inner kernels in ipc::detail, deducing
expression-templated front ends in ipc, and float alongside double.

Families that already had scalar-templated kernels but no front end (so a
matrix-row argument forced a Ref materialization per call, and an explicit
scalar produced an error wall inside Eigen): edge_edge_mollifier, point_plane,
and the three signed distances (line_line, point_line -- a 2D family -- and
point_plane). Families that were double-only with dimension-erased
VectorMax/MatrixMax signatures: closest_point, tangent_basis,
relative_velocity, and geometry/area. Their autogen kernels are templated with
the same instantiation-macro pattern as line_line; the only edits to generated
expressions are T() literal wrappers, verified byte-identical to the previous
text modulo the scalar substitution.

relative_velocity's runtime-dim entry points keep their exact public
signatures (template <typename T = double> over dim-templated kernels), so
call sites passing int dim compile unchanged. No caller anywhere needed
editing; the deducing front ends accept every argument type used in-tree.
relative_velocity ends up fully header-inline, so its TU is deleted.

Small hand-written kernels are header-inline; wide autogen bodies stay in
their TUs. That split is load-bearing, and the new "Converted families"
benchmark (tests/src/tests/benchmark_eigen.cpp) measured it both ways: with
the tangent kernels TU-defined, the dimension-erased path paid the Ref copies
and MatrixMax wrap at an opaque call boundary and point_edge_tangent_basis
REGRESSED 2x on matrix rows; header-inlining the value kernels turned that
into the wins below. Measured old-vs-new by interleaved A/B of two binaries
(baseline built from a worktree at the previous commit; controls 0.99-1.00x):

  point_edge_closest_point, rows           8.7  -> 1.8 ns   4.8x
  point_edge_closest_point, Vector3d       4.7  -> 1.7 ns   2.8x
  point_edge_closest_point_jacobian, rows 14.9  -> 6.2 ns   2.4x
  point_point_relative_velocity, rows      5.5  -> 1.4 ns   3.9x
  pp_relative_velocity_jacobian(dim)       6.8  -> 1.8 ns   3.9x
  edge_length, rows                        4.1  -> 1.3 ns   3.1x
  point_edge_tangent_basis, rows           7.1  -> 4.2 ns   1.7x
  point_triangle_tangent_basis, rows       7.7  -> 5.0 ns   1.5x

The already-fixed-size 3D functions (edge_edge/point_triangle closest point,
triangle_area, edge_edge_cross_squarednorm, point_plane_distance) measured
neutral, as expected: the win was always recovering the compile-time
dimension, not the templates themselves. One residual: point_point_tangent
basis on matrix rows reads 0.87-0.90x (its fixed-dim path improved 1.11x);
suspected branch/layout effects in its axis-picking body, unresolved.

Also: move the relative-velocity Γ layout derivations from stranded TU
comments into the doxygen of their public front ends, exempt NOTE/TODO/
WARNING/FIXME comments from clang-format reflow, and swap a leftover
fmt include for spdlog in the CCD benchmark test.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* Bind the distance and tangent kernels directly in Python

The public front ends deduce their scalar and dimension from the argument
expressions, so their address cannot be taken. Rather than wrap each one in a
lambda, bind the ipc::detail kernel with its scalar named explicitly --
&detail::f<double> -- which is a concrete function and needs no wrapper.

Two cases keep something else:

- point_plane_distance, _gradient and _hessian each have two arities (a plane
  given as origin+normal, or as three triangle vertices). Both remain bound
  under one Python name, disambiguated with py::overload_cast on the parameter
  list.
- edge_length_gradient, point_point_relative_velocity and
  point_edge_relative_velocity keep their lambdas. Their kernels are templated
  on the dimension, so any address-of would pin one; the lambdas take
  VectorMax3d and preserve the runtime 2D/3D dispatch these functions have
  always offered from Python.

Docstrings, argument names and Python-visible signatures are unchanged.

Verified against a freshly built ipctk (the first Python build of this work):
nose2 -s python/tests passes 95/95, and a targeted probe exercises all 40
converted entry points. The repo suite covers none of these functions, so the
probe is what actually checks them: both point_plane arities return the right
shapes (3-vector/3x3 versus 12-vector/12x12), the three retained lambdas still
accept 2D and 3D (shape (4,) versus (6,) from edge_length_gradient), the
runtime-dim jacobians work at dim 2 and 3, and values are correct -- signed
distance -1 where the unsigned distance is +1, edge-edge cross squared norm 16
for perpendicular length-2 edges.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

* Bind the remaining 3D distance kernels directly in Python

Applies the &detail::f<double> treatment to the bindings converted to lambdas
earlier on this branch: line_line, edge_edge and point_triangle. Their kernels
take Eigen::Vector3<T>, so naming the scalar is enough to get a concrete
function and the wrapper is unnecessary. The dtype parameters keep their
py::arg defaults, which bind fine against the kernel's required parameter.

Three groups deliberately keep their lambdas:

- line_line_distance_gradient and line_line_distance_hessian have no detail
  kernel to address. They are single-layer Eigen::MatrixBase templates, which
  is correct for them: they read three coefficients per argument and hand them
  to generated code, so there is no whole-vector operation whose size a second
  layer would need to recover.
- point_point, point_line, point_edge and point_edge_distance_type take
  VectorMax3d and dispatch on the dimension at runtime.
- The normalization_* family, likewise VectorMax3d.

Pinning a dimension in any of those would silently drop 2D from the Python API.

Verified against a rebuilt ipctk: nose2 95/95, the previous 40-point probe
still green, and a new 21-point probe covering the newly converted functions
and the retained lambdas. Both dtype spellings (defaulted and explicit) return
the same value, and every VectorMax3d entry point still answers in 2D and 3D.
Docstrings, argument names and signatures unchanged.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

* Document the geometry-kernel conversion in the release notes

Covers the three preceding commits: the two-layer conversion of the tangent,
closest-point, relative-velocity, area, mollifier, point-plane and signed
distance families; the measured speedups and the one unresolved regression;
the header-inline versus translation-unit split and why it is load-bearing;
and the Python bindings moving from lambdas to &detail::f<double>.

Also corrects two claims that the intervening work invalidated: the Highlights
line named only the distance, barrier and normal APIs, and the API Changes
section still advised wrapping in a lambda as the only way to take a function's
address.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

* Rename NormalizedBarrier's private scalar alias to avoid an MSVC clash

The private 'using T = typename BarrierT::value_type' shadowed the
template parameter of any derived class that also names its parameter T.
MSVC resolved 'NormalizedClampedLogBarrier<T>' inside PhysicalBarrier to
the inherited private typedef and rejected it as inaccessible, while
Clang and GCC resolved it to the derived class's own parameter.

* Allow the _v variable-template suffix in the clang-tidy naming check

is_eigen_expression_v, are_eigen_expressions_v, and dim_v follow the
standard library's convention for variable templates, which the
UPPER_CASE GlobalConstantCase rule rejects.

* Match the CI clang-format version to the pinned pre-commit hook

.pre-commit-config.yaml pins mirrors-clang-format v21.1.2, but the
format check ran clang-format 20. The two disagree on how to pack the
MatrixMax3 initializers in normal.hpp, so a file formatted by the hook
a contributor actually runs failed CI. The whole tracked tree is
already clean under 21.

* Key the CI build cache on the runner CPU

FindSIMD compiles with -march=native, so every cached object file carries
the building runner's ISA. The cache key was runner.os + config with no CPU
component, so objects built on one runner model were restored onto another
and the test step died with SIGILL across unrelated suites (friction,
candidates, CFL, plane-vertex collisions).

The run that populated the cache compiled from scratch in 4m58s and passed;
the next run restored 313 MB, built in 1m22s, and failed in 29s.

* Clean up release_notes.rst.

* Move low-level normal/distance templates into ipc::detail behind SFINAE-friendly front ends

Push the fixed-size, per-scalar implementations (point-line/triangle/line-line
normals, point/edge/triangle/plane distances, tangent bases, relative
velocities) into ipc::detail, and give each a thin ipc:: front end that takes
Eigen::MatrixBase<Derived> so overload resolution SFINAEs away cleanly instead
of hard-erroring on non-Eigen arguments. Drops the IPC_ASSERT_EIGEN_ARGS macro
and its is_eigen_expression_v/are_eigen_expressions_v traits now that the
MatrixBase parameter does that job directly. Copies the detail-side Doxygen
comments down to the public wrappers so the documented API carries its own
docs instead of pointing into an internal namespace.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

* Fix documentation

- Explicitly specify the global templated version of distance functions

---------

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>
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