Predictive coding matches backprop at 97.73% MNIST, 50x faster in C++
Deepity is a from-scratch C++ library (with Python bindings) that swaps backprop for predictive coding: each layer adjusts locally to its own prediction error instead of shipping one signal end to end. It hits 97.73% on MNIST in 60 seconds on a laptop CPU, within 1% of a PyTorch backprop baseline and about 50x faster than the author's earlier version. A new variant, DKPPCN, uses Direct Kolen-Pollack feedback alignment to settle in a single step instead of the usual 20-30.