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LightOn’s OPU (Optical Processing Unit) can do only one thing, but it can do this one thing fast and efficiently. It can multiply a vector with a giant random matrix. A special waveguide does the random matrix multiplication in an analog way. The random projection has a good property; it nearly preserves the distances because of the Johnson–Lindenstrauss lemma. OPU is used to reduce dimensions to create an easier problem (a 32 dimension vector is better than a 33600 dimension) which needs less storage, less computing capacity or a smaller neural network.