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The hinge loss function is defined as
:<math>V(f(\vec{x}),y) = \max(0, 1-yf(\vec{x})) = |1 - yf(\vec{x}) |_{+}</math>
The hinge loss provides a relatively tight, convex upper bound on the 0-1 [[indicator function]]. Specifically, the hinge loss equals the 0-1 [[indicator function]] when <math>sgn(f(\vec{x})) = y</math> and <math>yf(\vec{x})
While the hinge loss function is both convex and continuous, it is not smooth (that is not differentiable) at <math>yf(\vec{x})=1</math>. Consequently, the hinge loss function cannot be used with gradient descent methods or stochastic gradient descent methods which rely on differentiability over the entire ___domain. However, the hinge loss does have a subgradient at <math>yf(\vec{x})=1</math>, which allows for the utilization of subgradient descent methods. (cite Utah)
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