Who Invented Backpropagation?
Efficient backpropagation (BP) is central to the ongoing Neural Network (NN) ReNNaissance and "Deep Learning." Who invented it? BP's modern version (also called the reverse mode of automatic differentiation) was first published in 1970 by Finnish master student Seppo Linnainmaa [BP1] [R7]. In 2020, we celebrated BP's half-century anniversary! A precursor of BP was published by Henry J. Kelley in 1960 [BPA]—in 2020, we celebrated its 60-year anniversary. In the 2020s, it was still easy to find