Rendle, S. (2010). Factorization Machines. ICDM.
Key formula: y = w0 + sum_i w_i x_i + sum_{i<j} <v_i, v_j> x_i x_j,
with the O(nk) pairwise reformulation used by all fast implementations.
libffm — canonical C++ FFM implementation (logistic loss, OpenMP/SSE):
https://www.csie.ntu.edu.tw/~cjlin/libffm/
Note: libffm omits w0 and the linear term; we keep both (see math_spec.md).
xLearn — C++ LR/FM/FFM library: https://github.com/aksnzhy/xlearn
fastFM — existing FM library (name collision avoided: we are modern-fm)
DeepCTR-Torch — PyTorch CTR models including FM-family