*trsm: remove zero-RHS skip for consistent NaN on singular matrix#1301
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The left-solving non-transposed path in DTRSM/S/CTRSM/ZTRSM has an optimization that skips the division B(K,J)/A(K,K) when B(K,J) is exactly zero. When A(K,K) is also zero (singular matrix), this leaves B(K,J)=0 instead of computing 0/0=NaN, producing inconsistent results across different calling variants of the same triangular solve. Closes Reference-LAPACK#636
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langou
approved these changes
Jul 9, 2026
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The left-solving non-transposed path in DTRSM/S/CTRSM/ZTRSM has an optimization that skips the division B(K,J)/A(K,K) when B(K,J) is exactly zero. When A(K,K) is also zero (singular matrix), this leaves B(K,J)=0 instead of computing 0/0=NaN, producing inconsistent results across different calling variants of the same triangular solve.
Closes #636