Rumelhart, David E.; Hinton, Geoffrey E., Williams, Ronald J. (8 October 1986). “Learning representations by back-propagating errors”. Nature323 (6088): 533–536. doi:10.1038/323533a0.
"The most obvious drawback of the learning procedure is that the error-surface may contain local minima so that gradient descent is not guaranteed to find a global minimum." p.536 of Rumelhart, et al. (1986). Learning representations by back-propagating errors. Nature.
