Fix missing diagonal term in TransverseFieldIsing.from_qubo bias - #134
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The QUBO-to-Ising substitution x=(1+s)/2 requires the diagonal of the symmetrized QUBO matrix to appear in the linear bias h_q, not just in the row sums. Without it, h_q was systematically wrong and the solver would converge confidently to incorrect optima. Verified the fix by brute-force affine-consistency checks and by confirming the solver now recovers the true optimum end-to-end. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
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The QUBO-to-Ising substitution x=(1+s)/2 requires the diagonal of the symmetrized QUBO matrix to appear in the linear bias h_q, not just in the row sums. Without it, h_q was systematically wrong and the solver would converge confidently to incorrect optima. Verified the fix by brute-force affine-consistency checks and by confirming the solver now recovers the true optimum end-to-end.