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neural nets

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96 Jonathan Richard Shewchuk 17 Vanishing Gradients; ReLUs; Output Units and Losses; Neurobiology THE VANISHING GRADIENT PROBLEM; ReLUs [Last lecture, we put a logistic function at the output of every unit except the input units. These units are called sigmoid units. But in practice, sigmoid units are usually a poor choice for hidden layers.] Problem: When unit output s is close to 0 or 1 for most training points, s0 = s(1 s) ⇡ 0, so gradient descent changes s very slowly. Unit is “stuck.” Slow training.…

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