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the next section we will introduce the sigmoid and softmax tools for classifi- ... training examples. We will introduce the cross-entropy loss function. 4.An algorithm for optimizing the objective function. We introduce the stochas-tic gradient descent algorithm. Logistic regression has two phases: training: we train the system (specifically the weights w and b) using. Softmax Loss, Negative Logarithmic Likelihood, NLL ¶. Cross Entropy Loss same as Log Softmax + NULL Probability of each class. f ( s, y ^) = − ∑ c = 1 M y ^ c l o g ( s c) y ^ is 1*M vector, the value of true class is 1, other value is 0, hence. f ( s, y ^) = − ∑ c = 1 M y ^ c l o g ( s c) = − l o g ( s c). The softmax function transforms a vector K of real values into a vector K whose elements range between 0 and 1 and sum up to 1. This function is also called softargmax or multi-cast logistic regression. The advantage of applying this function is that the transformed vector values can be interpreted as a probability and, if an input is negative.