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From "wangwei (JIRA)" <j...@apache.org>
Subject [jira] [Created] (SINGA-316) Add SigmoidCrossEntropy
Date Tue, 23 May 2017 02:44:04 GMT
wangwei created SINGA-316:
-----------------------------

             Summary: Add SigmoidCrossEntropy
                 Key: SINGA-316
                 URL: https://issues.apache.org/jira/browse/SINGA-316
             Project: Singa
          Issue Type: New Feature
            Reporter: wangwei
            Assignee: wangwei


SigmoidCrossEntropy is a loss function for samples with multiple labels.
For each sample, denote the final layer's output as x (a vector of length L), 
and y as the ground truth label vector (a binary vector of length L) 
where L is the label set size. 
SigmoidCrossEntropy computes 
p_i = sigmoid(x_i)
loss_i = -y_i log p_i -(1-y_i)log (1-p_i)

A threshold t_i can be tuned to decide the label assignment, e.g. y_i = 1 if p_i > t_i.



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