refac: clean up piecewise module (#641)

* refac: use _to_linexpr in tangent_lines instead of manual dispatch

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* refac: rename _validate_xy_points to _validate_breakpoint_shapes

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* refac: clean up duplicate section headers in piecewise.py

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* refac: convert expressions once in _broadcast_points

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* refac: remove unused _compute_combined_mask

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* refac: validate method early, compute trailing_nan_only once

Move method validation to add_piecewise_constraints entry point and
avoid calling _has_trailing_nan_only multiple times on the same data.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* refac: deduplicate stacked mask expansion in _add_continuous_nvar

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* refac: remove redundant isinstance guards in tangent_lines

_coerce_breaks already returns DataArray inputs unchanged.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* refac: rename _extra_coords to _var_coords_from with explicit exclude set

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* refac: clarify transitive validation in breakpoint shape check

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* refac: remove skip_nan_check parameter

NaN breakpoints are always handled automatically via masking.
The skip_nan_check flag added API surface for minimal value —
it only asserted no NaN (misleading name) and skipped mask
computation (negligible performance gain).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* refac: remove unused PWL_AUX/LP/LP_DOMAIN constants

Remnants of the old LP method that was removed.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* refac: always return link constraint from incremental path

Both SOS2 and incremental branches now consistently return the
link constraint, making the return value predictable for callers.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* refac: split _add_continuous into _add_sos2 and _add_incremental

Extract the SOS2 and incremental formulations into separate functions.
Add _stack_along_link helper to deduplicate the expand+concat pattern.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* refac: rename test classes to match current function names

TestPiecewiseEnvelope -> TestTangentLines
TestSolverEnvelope -> TestSolverTangentLines

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* refac: use _stack_along_link for expression stacking

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* refac: use generic param names in _validate_breakpoint_shapes

Rename x_points/y_points to bp_a/bp_b to reflect N-variable context.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* refac: extract _to_seg helper in tangent_lines for rename+reassign pattern

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* refac: extract _strip_nan helper for NaN filtering in slopes mode

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* refac: extract _breakpoints_from_slopes, add _to_seg docstring

Move the ~50 line slopes-to-points conversion out of breakpoints()
into _breakpoints_from_slopes, keeping breakpoints() as a clean
validation-then-dispatch function.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* fix: resolve mypy errors in _strip_nan and _stack_along_link types

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* refac: remove duplicate slopes validation in breakpoints()

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* refac: move _rename_to_segments to module level, fix extra blank line

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* test: add validation and edge-case tests for piecewise module

Cover error paths and edge cases: non-1D input, slopes mode with
DataArray y0, non-numeric breakpoint coords, segment dim mismatch,
disjunctive >2 pairs, disjunctive interior NaN, expression name
fallback, incremental NaN masking, and scalar coord handling.

Coverage: 92% -> 97%

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* fix: resolve ruff and mypy errors

- Use `X | Y` instead of `(X, Y)` in isinstance (UP038)
- Remove unused `dim` variable in _add_continuous (F841)
- Fix docstring formatting (D213)
- Remove unnecessary type: ignore comment

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: 3 people

doc/piecewise-linear-constraints.rst

@@ -50,7 +50,6 @@ API
         method="auto",  # "auto", "sos2", or "incremental"
         active=None,  # binary variable to gate the constraint
         name=None,  # base name for generated variables/constraints
-        skip_nan_check=False,
     )
 
 Creates auxiliary variables and constraints that enforce all expressions

linopy/constants.py

@@ -46,9 +46,6 @@
 PWL_FILL_SUFFIX = "_fill"
 PWL_BINARY_SUFFIX = "_binary"
 PWL_SELECT_SUFFIX = "_select"
-PWL_AUX_SUFFIX = "_aux"
-PWL_LP_SUFFIX = "_lp"
-PWL_LP_DOMAIN_SUFFIX = "_lp_domain"
 PWL_INC_BINARY_SUFFIX = "_inc_binary"
 PWL_INC_LINK_SUFFIX = "_inc_link"
 PWL_INC_ORDER_SUFFIX = "_inc_order"