title: Implementing contrastive loss and triplet loss in Tensorflow
body: <p>I started to play with TensorFlow two days ago and I'm wondering if there is the triplet and the contrastive losses implemented.</p>
  
  <p>I've been looking at <a href="https://www.tensorflow.org/versions/r0.9/api_docs/python/nn.html#losses" rel="noreferrer">the documentation</a>, but I haven't found any example or description about these things.</p>