[MRG] Compute value in ot.solve_sample with reg and lazy=True

[itzzdev09]

Types of changes

• Bug fix

Description

ot.solve_sample(X_a, X_b, a, b, reg=..., lazy=True) returns an OTResult whose value is None: the lazy regularized branch sets value_linear, the potentials and the lazy plan, but never the regularized value. Because of this, the debiased lazy Sinkhorn divergence fails:

import numpy as np, ot
rng = np.random.RandomState(0)
xs, xt = rng.randn(6, 2), rng.randn(5, 2) + 1
ot.solve_sample(xs, xt, reg=1.0, lazy=True).value               # None
ot.solve_sample(xs, xt, reg=1.0, lazy=True, debias=True).value  # TypeError: unsupported operand type(s) for +: 'NoneType' and 'NoneType'

The value is now computed as in the non-lazy ot.solve (value_linear + reg * R(plan), with R the KL to a b^T or the negative entropy). The plan is read from lazy_plan in batches of batch_size rows, so memory use stays O(batch_size × n_b).

The lazy solver is always the entropic Sinkhorn, so it now raises NotImplementedError for another reg_type (for example "L2") instead of silently solving a different problem, as the non-lazy path already does for unsupported values.

How has this been tested

Added test_solve_sample_lazy_value, which checks value against the non-lazy solver for reg_type "KL" and "entropy" (with batches smaller than the problem), and for debias=True and "split". It fails on master. test/test_solvers.py passes (337 passed, 5 skipped).

Checklist

• I have added tests to cover my changes.
• I have updated the RELEASES.md file.

[codecov]

Codecov Report

❌ Patch coverage is 93.54839% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 95.37%. Comparing base (10c74a1) to head (5dd8c6b).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #861      +/-   ##
==========================================
- Coverage   96.86%   95.37%   -1.49%     
==========================================
  Files         128      128              
  Lines       26181    26212      +31     
==========================================
- Hits        25359    25001     -358     
- Misses        822     1211     +389     

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.