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…al_multiply_cpu When beta=0, the BLAS specification states that matrix C may be uninitialized and its contents must not be read. COSMA violated this in two places: 1. multiply.cpp split_k path: iterations K>0 set beta=1 to accumulate partial results, but the C buffer from the memory pool was never initialized. With NaN/Inf in uninitialized memory, this produces garbage results (0*NaN=NaN per IEEE 754, and 1*NaN=NaN for K>0). 2. local_multiply_cpu: `Cvalue *= beta` reads C even when beta=0. Per IEEE 754, 0.0 * NaN = NaN, so this corrupts the output. Fix: (1) zero-fill C before the split_k loop when beta=0 and divisor>1, (2) use conditional assignment in local_multiply_cpu. Add regression tests (BetaZero/FloatUninitialized, DoubleUninitialized) that fill C with NaN and verify beta=0 produces correct, NaN-free results. Found while debugging sporadic segfaults in CP2K AIMD with GPU-accelerated COSMA (parallel_gemm called with beta=0 from make_basis_lowdin). PR eth-cscs#159 (v2.8.0) partially addressed this in multiply_using_layout but did not cover the internal split_k accumulation or local_multiply_cpu. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Ref #158
Accept unitialized matrix C for case beta==0, fill with zeros on entry to call to
multiplyNeed to wait for a new release of COSTA, with a routine to fill matrix with given value.