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NNUE
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=NN Structure=
The neural network of Stockfish NNUE consists of four layers, W1 through W4. The input layer W1 is heavily overparametrized, feeding in the [[Board Representation|board representation]] for various king configurations.
The efficiency of the net is due to [[Incremental Updates|incremental update]] of W1 in [[Make Move|make]] and [[Unmake Move|unmake move]],
where only a fraction of its neurons need to be recalculated. The remaining three layers with 32x2x256, 32x32 and 32x1 weights are computational less expensive, best calculated using appropriate [[SIMD and SWAR Techniques|SIMD instructions]] like [[AVX2]] on [[x86-64]], or if available, [[AVX-512]].
