Forward: hand-written tiled GEMM vs cuBLAS sgemm on random matrices
(square / non-tile-aligned rect / 256³), max relative error < 1e-3, using
the row-major⟺col-major identity to drive cuBLAS without explicit
transposes. Backward: scalar loss L = sum(W∘C) (so dC = W), dA/dB from
matmul_backward checked against the finite-diff harness. Gated behind
not(no_cuda).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
New xtrain-tensor crate: DType (F32), shape/stride helpers, Arc-counted
host/device Storage with CPU↔CUDA copy, and a contiguous Tensor with
creation, host↔device transfer, and a scale() op driving the elementwise
kernel. GPU integration tests (host↔device roundtrip + scale correctness)
gated behind not(no_cuda); a thin build.rs emits the no_cuda cfg so the
kernel call sites compile out locally.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
