wegamekinglc / Derivatives-Algorithms-Lib / 28696575569

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master: 85%

Pull #197

github

Fix out-of-bounds write in dense SymmetricDecomposition::QForm

SymmetricDecomposition_::QForm (dal-cpp/dal/math/matrix/sparse.cpp) declared
its work vector 'wij' empty and then passed it to Solve, whose dense
Cholesky XSolve_af implementation writes (*x)[ii] for ii in [0, Size())
without resizing. Any non-trivial dense QForm call therefore wrote off
the end of wij, corrupting memory.

The fix mirrors the banded QForm override (dal-cpp/dal/math/matrix/
banded.cpp), which already pre-sizes its work vectors to Size() and
REQUIREs j_mat.Cols() == Size(). Two changes only: add the REQUIRE,
and Vector_<>
 wij; -> Vector_<>
 wij(Size());. XSolve_af and the
caller-side pre-size convention are left untouched.

Adds a regression test (dal-cpp/tests/math/matrix/test_sparse_qform.cpp)
that exercises the dense path end-to-end via CholeskyDecomposition(W)
(which returns a Cholesky_ that does not override QForm) and checks
dst == J W^{-1} J^T against an independent per-row Solve reference.
Before the fix this test aborts (OOB); after, it passes.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

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