Gahow Wang
9ca98efd98
New xtrain-autodiff crate with a reusable central finite-difference gradient check: grad_check(x, shape, f, analytic_grad, cfg) compares an analytic gradient against (f(x+ε)-f(x-ε))/2ε per element with a relative tolerance. Host-only (no CUDA): the loss closure owns any GPU work, so T4's per-op backward checks can reuse it directly. Includes host unit tests (sum(x²) grad 2x passes; a wrong grad is rejected). Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>